Unit 731 and the Human Skulls Discovered in 1989: Physicians Carrying Out Organized Crimes


Tsuneishi Kei-ichi



Brief History of Unit 731


          The Tôgô Unit


          Unit 731 was officially inaugurated in the town of Ping Fan (near Harbin) in China in August of 1936[1].  Preparatory activities were already underway in the fall of 1932, however, in a shoyu [soy sauce] factory in a small village about 100 kilometers southeast of Harbin[2].  In that year (1932), Ishii Shirô, the man who would later become the head of Unit 731, launched and became the director of the Army Medical College’s Epidemic Prevention Research Laboratory (EPRL) in Tokyo[3].  For the next year, besides the official activities in EPRL, Ishii was heading up the construction of the unit headquarters in China.  Experiments on human beings began in the fall of 1933 as an inner activity within the Kantô Army[4].  The researchers who participated in these operations were all military physicians and each used an alias.  This unit was called by the code name Tôgô, after the alias Ishii used at that time.  The use of aliases was indicative of how much importance they attached to maintaining the secrecy of their activities.        

EPRL was the control center and the Tôgô Unit (as well as its successors such as Unit 731 and related units) would carry out its commands—including experiments on humans.  Another key function of the Laboratory was to serve as a link between civilian research facilities and military ones such as Unit 731.

          Two factors contributed to the necessity of maintaining secrecy about operations during the three years after 1933.  One factor was that they wanted to hide the purpose of the unit’s organization:  they were performing experiments on humans.  The second factor was that, because this facility was doing research on human beings as part of a feasibility study, the responsibility would not extend to the emperor if they either failed or were found out.  Failures on the part of the Emperor’s military would tarnish the image of the Emperor’s infallibility, and for members of Japan’s army at that time such a thing was impermissible.


          The aim of the feasibility study for conducting experiments on humans had two aspects:


          (1)     To find the possibility of the continuous procurement of test subjects and determine whether the continuous experimentation on humans was possible.

(2)              To make sure that Ishii’s project--experiments on humans for the development of biological weapons--was worthwhile.


          Experiments to inoculate people against the illness associated with anthrax germs were already being carried out in the operations up to 1936.  Of greater note were the methodical experiments on humans with cyanide.  Approximately 10 people were subjected to these experiments each time they were performed[5].

          Six times from 1934 to 1936, the project directors had the test subjects drink cyanide and observed the circumstances leading to their deaths.  The following procedures were characteristic of these cyanide experiments on humans:


          (1)     Photographs were taken.

          (2)     Autopsies were performed.

          (3)     Verification of a lethal dose was noted.

          (4)     The cyanide was mixed with beer, wine or coffee.

          (5)     The subjects were Russian spies (derogatorily known as Russkii’s) as well as spies that the Special Service Agency used and deemed no longer necessary.


          Steps 1-3 show that experiments were performed not for murdering the victims, but perusing some “medical” purposes.  The motivation for procedure 4 was to make the subjects drink the difficult-to-swallow cyanide without any resistance and without causing them any apprehension about being made to drink a toxic substance.  The use of spies—step 5--indicates that the procurement of test subjects thought to have begun after Unit 731 was established actually began during the period of the Tôgô Unit.

          The medical objectives of the cyanide experiments were, except for procedure 3, to determine the effect murder by cyanide had on the human body.  We can surmise this from the testimony of Okamoto Kôzô[6], a scholar of pathology from Kyoto University, at an investigative council held in July of 1948.


The unit physicians inoculated about 15 prisoners at one time. In order to study the conditions of the patients’ illness they murdered them on 3rd day, 4th day, and so on after its onset and before death, and then performed autopsies on the corpses.  The bodies had most likely been poisoned with potassium cyanide since the cause of death was suffocation, but because Okamoto was only directly to perform research on the subjects after they were dead, he had no idea who these poisoned criminals were.


Cyanide was not the only substance used; other researchers used chloroform.  Onodera Yoshio, who had performed experiments on humans in Unit 1644 in Nanjing, provided the following testimony on July 24[7]:


We performed studies on approximately 100-150 people.  Satô Shunji analyzed the logs [term used to refer to human subjects—Editor] and Onodera performed research on the developmental conditions of tuberculosis.  In the end we injected them with chloroform and put them to sleep.  They died from the injection.  During his tenure there, they did not use potassium cyanide.  (underline in the original text-Ed)


          In 1947, Kasahara Shirô, who performed experiments on humans who had epidemic hemorrhagic fever (EHF, now called hemorrhagic fever with renal syndrome) in Unit 731, responded to an American inquiry about this by saying that “he put them to sleep with chloroform.”[8]

          Some physicians murdered their victims with potassium cyanide, and then dissected them, while others used chloroform.  It may be assumed that these different approaches were due to the experiments’ objectives.  We can surmise that the reason they performed potassium cyanide experiments to such an extent when the Unit was first created was that they were looking for a method to murder their test subjects which, before beginning their real research, would not contradict the medical data. Scrupulous precautions are a requirement of all research, but how should we judge the scrupulosity shown in these instances—cases where the goal is the opposite of usual research?  It is obvious how extremely narrow the perspective of these “specialized fools” had become.  But this circumstance is also emblematic of how frightening it is when researchers go deeper and deeper into the particulars of their work while becoming more and more distant from what is common sense in ordinary society.




          Official Start of Unit 731


          In August, 1936 Unit 731 was created as a formal unit of the Japanese army and the Tôgô Unit ceased to exist.  The center of operations was moved to facilities built about 30 kilometers south of Harbin.  These facilities not only had medical research and experimentation rooms but were also furnished with places for interning test subjects, that is a jail (wards 7 and 8).  The research and experimentation rooms were built to surround the jail and the researchers performed their daily research while watching over the test subjects[9].

          There was no change in the level of “scrupulous precaution” after Unit 731 came into existence.  The procurement of test subjects for Unit 731 was entrusted to the military police and the Special Service Agency.  According to the Unit’s demands, a health exam determined when people would be sent to the Unit by either[10].

          The group in charge of test subjects was headed by physiologist Yoshimura Hisato who joined the Unit from Kyoto University in 1938.  He was called the “Scientific Devil” within the Unit.  The group Yoshimura headed was composed of two sections each with two subgroups.  One section carried out medical exams and the other was in charge of supervising prisoners, dispatching prisoners to experimentation rooms and processing their admission to the Unit.  The heads of the two sub-groups in charge of the medical exams were both physicians.  One of those, Miyagawa Tadashi, joined Unit 731 in April 1944.  He was in charge of X-rays of the test subjects.  After the war he became a professor in Tokyo University’s Medical Department and lived to the age of 88.  His obituary stated, “Miyagawa led a life that pioneered the medical use of radiation.  He contributed to the development of the medical use of the cyclotron to treat brain tumors and other diseases.”[11]  The second sub-group was in charge of blood and immunity exams as well as the health maintenance of test subjects.  Not everyone sent to Unit 731 was subjected to experiments.  These were only carried out on healthy people, and after they were accepted into the program, the maintenance of their health was a priority.

          Why did Yoshimura become the head of this group?  He was a physiologist. Physiology is a counterpart of  pathology, the study of the etiology of illness.  There were four pathologists in Unit 731.  Their task was to determine whether a prisoner’s cause of death during an experiment in which he had been infected with a pathogen was actually due to the pathogen.  The field of physiology, on the other hand, pertains to understanding why a living being is.  Yoshimura wrote, “The purpose of a physiologist’s scholarship is to scientifically explain from a variety of aspects what the phenomenon of a normal life is.” (italics in the original)[12] Physiology is the academic discipline that studies the characteristics of human health.  Therefore, Yoshimura might take responsibility for departments that controlled wards 7 and 8.

          In these wards medical exams were carried out with scientific rigor to determine how a test subject could finally be killed.  However, a rigorously “scientific” mentality which does not take into account the dignity of its victims as human beings—which ignores such values—is perverse science.  In the case of Unit 731 it is not difficult to make this judgment; it is not difficult because the perversion of science in Unit 731 was obvious.  But recently it seems that a more subtly perverse science is being put before us.  Taking shape in ways more difficult for us to recognize, it too disregards the value of human beings and reverses what science should be.  An example is human cloning which masquerades as “therapy for infertile persons.” 

The military personnel of Unit 731, who were not themselves physicians, referred to Yoshimura as a “Scientific Devil.” A person who photographed the progress of experiments on humans testified:[13]


In the spring of 1944 there were prisoners on the second floor of ward 7.  About seventy of them taking keys off a guard and singing revolutionary songs created quite a disturbance.  All of them were killed with gas.  Yoshimura, who was in Kobe at the war, was a scientific devil, a cold-blooded animal.


According to testimony, many of prisoners were undergoing various experiments, so they made gas attack to retain experimental data of them. Yoshimura was not only called a “devil” because of the strictness with which he conducted experiments.  He also soaked the fingers of a 3-day old child in ice water (ice and salt).

          There were several hundred prisoners in the jails of Unit 731 in the summer of 1945 after Japan was defeated.  Every one of them was murdered.  The following testimony describes those circumstances:[14]


On August 11 and 12, after the end of the war approximately 300 prisoners were disposed of.  The prisoners were coerced into suicide by being given a piece of rope.  One quarter of them hung themselves and the remaining three quarters who would not consent to suicide were made to drink potassium cyanide and killed by injection.  In the end all were taken care of.  The prisoners were made to drink potassium cyanide by mixing it with water and putting it into bowls.  The injections were probably chloroform.


The murdered people were cremated and buried at the facilities of Unit 731.



The Human Skulls Discovered in 1989


          In July 1989 a great quantity of human bones was discovered in Tokyo at the construction site for the Ministry of Health and Welfare’s Research Center for Preventive Hygiene.  This area had been the home of the Army Medical College from 1929 until 1945.  The police first announced that bones were from 35 bodies, but in 1992 Sakura Hajime, an expert involved with the case, announced that those were from more than 100 bodies[15].  He said the bones were those of people of Asian descent, but not of just one ethnic group.  Several ethnic groups were intermingled.  Moreover, the bones were not over one hundred years old; they had been there for more than 15 years.

          Sakura’s data indicated that the bones found in 1989 were those of foreigners of Asian descent who had been buried during the period in which the Army Medical College was located there.  The fact that they were buried did not mean that they had been interred there formally but that they were hidden to suppress evidence.  This was the same method of disposal used by Unit 731 on murdered test subjects.

          The police treated the discovery of the bones as they would any dead body or bodies by investigating the cause of death and events leading up to it.  But a week after the bones were discovered, the police announced that they uncovered no evidence about the events surrounding their deaths.  They concluded that even if these people had been victims of a crime, they had been in the ground for over 15 years and the statute of limitations had passed.  They concluded that the remains were those of people who had been found dead on the street and disposed of in this manner.

          The truth was different.  Sakura’s investigation made two points clear:[16]

          (1)     There were marks on most of the skulls that led him to believe that they had been severed with a scalpel or a saw during practice brain surgeries at an experimental stage.  The bones had been in the earth for over fifty years, but in Japan in the 1940’s, brain surgeries which severed a part of the skull had not yet been performed.

          (2)     There were gashes from a sword on several of the skulls and others had been pierced by bullets from a pistol.

          Sakura’s first point indicated that the skulls had either been used for experimentation or practice where brain surgeries were performed.  The second of Sakura’s points suggested that they were victims of crimes, at least medical crimes.

          There is no direct connection between these experiments or crimes and Unit 731.  What these bones do indicate is that the barbarism of Unit 731 did not stand out as anything exceptional among military doctors in Japan. We can presume that these bones mean that physicians in the Japanese army practiced upon or performed experiments on the brains of people on the battlefield, or that physicians who had some relationship with the Army Medical College did, and that the evidence was destroyed and buried there.

          The testimony of Ken Yuasa, an army physician, supports this conjecture[17].

          According to Yuasa’s testimony, in order to quickly prepare physicians trained primarily as internists for the work needed as surgeons on the battlefield, they were gathered together every few months to perform atrocities called “surgery drills” on the battlefields of China.  They would capture citizens, shoot them in the thigh with a bullet, and undertake drills to see how long the extraction of a bullet would take.  If someone were frostbitten, they would perform an operation to sever the frostbitten part.

          These surgery drills were not just limited to one region of the country, but practiced widely.  In most cases the victims were locals arrested by the military, and delivered to the Army’s medical division.  This indicates that the surgery drills were not performed according to individual whim but that the army military division and military police undertook these activities methodically within the entire army.  It is likely that the skulls obtained from surgery drills were collected and sent to the Army Medical College under the control of the army physicians.  If this is the case, the skulls were definitely those of victims of war crimes.


Open Secret


          In my own research published in 1981, after analyzing research reports from 1943 and 1944 concerning hemorrahagic fever with renal syndrome published by Kitano Masaji (Ishii’s successor as unit director from August 1942 to May 1945) and other researchers, I concluded that their results were based on experiments done on human beings.  I substantiated that Yoshimura performed experiments on humans in his laboratory work on frostbite[18]. It was not difficult to prove their experiments on human beings through analysis their papers published by themselves. It needed only few medical knowledge. So any qualified physician could have reached the same conclusions as mine from those reports.

          Kitano contributed to an article about hemorraghic fever with renal syndrome in publications for the Defense Agency in 1969.  He wrote, “Smordentiv was not able to infect standard experiment animals such as mice, marmots, rabbits, and monkeys with either the blood or urine of patients.  He too performed experiments on humans to do research on the etiology of diseases.”[19] (author’s emphasis)  Smordentiv was a Soviet researcher who worked on EHF in 1940s and identified the virus for experiments on humans.  In Kitano’s 1969 recollections, he also confessed to having performed experiments on humans, as the other researcher had.  The results of these reports were announced in Defense Agency publications in which Kitano  did not try to hide that experiments had been performed on human beings.

          In 1968, the year before Kitano’s publication, Ikeda Naeo, a physician with Unit 731, published his own research in a paper entitled “Experimental Studies on Epidemic Hemorrhagic Fever: Pediculus Vestimenti and Xenopsylla Cheopis as Suspected Vectors of the Disease.”[20]  According to this report, experiments having to do with infections were carried out in the Army Hospital in Kokka on the border between China and the Soviet Union in January 1942.  These experiments on humans confirmed that EHF was carried by lice and fleas to the local people.  Five percent of the people who were infected with the disease died.  This unequivocal report, which admitted that human experiments had been performed with pathogenic inoculations that can cause death passed the inspection of referees and was published in a scholarly journal.  That experiments on humans had taken place in Unit 731 was self-evident to Ikeda and to the Association for Infectious Diseases that accepted his research.  It was the acquisition of data difficult to obtain without human experiments that was important rather than any ethical issues.  But because the research was never confirmed by recreating the experiments, it was meaningless.


          Yoshimura, the “Scientific Devil” of Unit 731, wrote: “My research during the war was published in English journals of physiology after the war and influenced European and American scholars.  Present-day research that evolved from my own is performed not only in Japan but also in universities and research centers worldwide and has produced results.”[21]  Yoshimura conducted research during the war at Unit 731 in China on low temperature physiology, including the elucidation of mechanisms concerned with frostbite.  After the war ended, he organized the Japanese Society of Biometeorology; his China research was the beginning of his work on how physiology relates to environmental stress.

          Articles Yoshimura published in English in the Journal of Japanese Physiology reported how humans reacted to zero-degree water[22].  The experiments had consisted of soaking the middle finger of the right hand in zero degree water and then observing the changes in skin temperature for 30 minutes.  Approximately 100 Chinese men and women between the ages of 15 and 74 were the subjects of these experiments.  “Approximately” is Yoshimura’s own word, which raises doubt about the rigor of the experiments.

          Yoshimura’s English article was criticized in newpapers and elsewhere because of the statement, “We performed experiments by soaking 3-day old infants in zero-degree water.”  Yoshimura and his fellow researchers responded, “Though detailed studies could not be attained on children below 6 years of age, some observations were carried out on babies.  ...the reactions were detected on the 3rd day after birth, and it increased rapidly with the lapse of days until at last it was nearly fixed after a month or so.”  Data was recorded about the physiological reactions of a child for 30 minutes on the 3rd day, first month, and a sixth month when the child’s middle finger was soaked in ice water.

          When a reporter from the Osaka office of the Mainichi Shimbun [Newspaper] contacted Yoshimura by telephone for a report on the infant experiments, he responded:  “Everyone misunderstands.  I’m being criticized for having done experiments on infant, but this was the child of the staff of Yakudai (Pharmaceutical College) who had been sent to the Unit.  They were experiments to investigate what kind of physiological reactions take place in the blood vessels when the skin is touched by cold water and from what point there is resistance to this and what we can do in this situation.  I used the child of my staff with his own encouragement.  The child was not the child of prisoner.”[23]  He then related how excited the staff all was about this research and that it was their eagerness that allowed them to offer their child to the experimental body.  That Yoshimura said the child he used for the experiments were not the child of prisoner but the child of his staff indicates that he was aware that these experiments were not usual practice.

          Should we forgive the parents their excessive enthusiasm in giving their 3-day old infant up to experiments?  What does it mean that these people participated in experiments and did research as scientists?  I don’t accept Yoshimura’s explanation to the reporter: everything can be forgiven as a misunderstanding because there was “enthusiasm” for his scientific research.  Yoshimura showed his lack of understanding in the way he replied to the reporter.  All the staff members in Yoshimura’s account have died and we can no longer ascertain the truthfulness of his explanations.

          If we accept Yoshimura’s claim that the child were not the child of prisoner, a different problem arises:  why didn’t he use his own children?  According to Yoshimura’s memoirs, Seventy-seven Years in Retrospect, he had four children.  Among those four, two were born before he went to Unit 731 and two were born while he was at the Unit.  If we follow Yoshimura’s own logic, the reason he didn’t offer his children to their experiments was because he was not enthusiastic about his own research.

          But the fact of the matter is that Yoshimura did not use his assistants’ child: he used the child of people who had been captured by the Unit.


          The three researchers I have just told you about did not try to hide their experiments on humans.  When I first began researching Unit 731, I anticipated enormous work exposing these experiments.  However, as we see in investigating Kitano’s The History of Army Hygiene During the Greater East Asia War, much can be accomplished with a little bit of effort; we can say it was easier than expected.  We can also say that most of the researchers in Unit 731 were not involved in a special cover-up about the experiments in which they took part.  While they have never revealed their crimes to society to criticiz themselves, they have discussed and revealed various facts within their own medical field.  Consequently, it has not been difficult to be certain—especially in terms of research pertaining to EHF and frostbite—-about who did what kind of human experiments.

          Because almost everyone in the Japanese medical world knew about the experiments on humans in Unit 731[24], the researchers in the Unit were able to report later on their own work in medical papers:  even after the war, reports were published that were unmistakably about the results of experiments on humans, and reminiscences about the Unit were written up in medical journals.  From this we can be certain that everyone in the Japanese medical community knew about the experiments of Unit 731.


Organized Crimes


          Even in the 21st century, the Japanese medical community continues to ignore the barbarism doctors committed between 1930 and 1945.  After 1945 the community showed indifference toward articles published in medical journals based on data obtained through barbaric practices.

          It would be a mistake for us to attribute this solely to the insensitivity of the Japanese medical community.  There is an institutional problem; it is not just the independent actions of Yoshimura, Okamoto and others.

For example, professors from Kyoto University and Tokyo University were the subjects of the American army’s inquiry into Unit 731’s experiments[25].  These professors were not members of Unit 731, but they were senior consultants to Ishii’s Tokyo research site, EPRL.  At Ishii’s request, they sent these students Yoshimura and Okamoto to the Unit, knowing that they would perform experiments on humans.

           The experiments on frostbite that Yoshimura performed were central to his research at Kyoto University.  Ishikawa Tachiomaru, who was dispatched to the unit at the same time as Yoshimura, wrote: “When an epidemic was raging in Manchuria’s Nôan area, we performed autopsies on 57 corpses which had been stricken with the disease.  This was a world record in terms of the number of corpses...”[26]  Kiyono Kenji, one of Ishikawa’s teachers, sent his students with the hope that they would research  diseases there with few cases in Japan.

          The truth is that teachers like Kiyono intended for their students to perform experiments on humans.  The students carried out this barbarism--which couldn’t be done in Japan proper--in China, Japan’s colony.  The wishes of the teacher were communicated to the students in China through EPRL and the results of those experiments were sent back to their teacher through the same channel.


          What are we to make of the fact that none of this was a secret in the medical world but was unknown for so long in the non-medical world?  It is possible that people in the medical world didn’t feel there was a reason to “expose” or “reveal” something that was not a secret.  Even if this is true, we must strongly denounce the insensitivity of ignoring the highly unusual nature of performing experiments on humans--experiments hidden from the non-medical world.  Or, to look at it another way, if the experiments continued to be hidden because of their unusual nature, this means there has been no change in the sense of privilege and authority physicians demonstrate even after they had been informed of the experiments performed on humans by their fellow physicians.

But once we look back their activities, we find the probability is great that physicians have not felt obligation to hide anything in particular about their experiments on humans during and after the war. It might be the reason to prove human experimentation in the Unit through papers quite easily. We’re forced to conclude that though people outside the medical world consider it an act of atrocity if they were victimized, tested upon or murdered this way, people within the medical community who do this as everyday work might not consider these acts to be unusual in any way.

          These murderous experiments were performed within a network formed by the Army’s Unit 731 and the national medical colleges with EPRL as the mediator.  The murderers were the physicians in the army research facilities, but it was not just the physicians who received the “benefits” of these acts; it was also the public researchers who were their teachers.  Excuses for their behavior took the following forms: (1) researchers who actually dirtied their own hands with these experiments did it for the nation and the army and (2) their actions contributed to the progress of science and medicine.    

          Without consulting anyone, the medical world took upon itself the right to decide all these things, and forced the “results” of their research on society.  But isn’t this the situation today as well?  I’d like to emphasize that it’s not a question of research “results” being good or bad, but rather a societal deficiency in which the medical community determines how those “results” are achieved.  I’m troubled that we continue to ignore the barbarism of the 20th century even now in the 21st century.  And I’m concerned that this is an indication that the Japanese medical community is neglecting its social responsibilities.  This is not just an issue of whether overt barbarism like that which existed at Unit 731 could possibly occur again, but the fact that we still lack the means to discover and prevent barbarism in a more subtle form from occurring.




Translated from Japanese by Stephen Miller

Revised the translated text by Tsuneishi Kei-ichi

[1] Brief History of the Kwantung Army Epidemic Prevention and Water Supply Section. On April 6, 1982, this was submitted to the Diet by Ministry of Health and Welfare.

[2] Endo Saburo, I and 15year war with China, Nicchu Shorin Co., 1981

[3] Fifty-year History of the Army Medical College, 1936, Army Medical College

[4] Endo, ibid

[5] Kai’s note; Kai’s notes recorded every day the report by each investigator on Teigin’s (Imperial Bank) case that is a bank robbery incident in Tokyo in January, 1948, by Kai Bunsuke chief of 1st section of investigation of the Metropolitan Police Department. Teigin’s case was an incident in which 12 persons were killed with cyanide and money was taken. The researchers on toxic in the former Japanese Army and members of Unit 731 were suspected. But in August, a painter was arrested and was sentenced to death. He had denied his commitment to Teigin’s case until his death of 95 years in the hospital prison in 1992.

[6] Kai’s Note

[7] op.cit

[8] Hill & Victor Report, Summary Report on B.W. Investigations, December 12, 1947, Edwin V. Hill, Chief, Basic Sciences, Camp Detrick. The other investigator was Joseph Victor.

[9] Interview with Dr. Akimoto Sueo by Tsuneishi, Akimoto had been a member of the unit since 1944 to research on serology without human experimentation and gave up to be a researcher, if he wanted he would be back to Tokyo University, after returning to Japan on account of his regret that he had not been able to be opposite others’ experimentation on human.

[10] Kai’s Note

[11] Mainichi Shinbun (Mainichi News), January 4, 2002

[12] Yoshimura Hisato, Seventy-seven Years in Retrospect (Kijukaiko), Celebration committee for his 77 years old Memoir, 1984

[13] Kai’s Note, and Interviews with Dr. Meguro Masahiko from 1981 to 1988

[14] Kai’s Note

[15] Sakura Hajime, The report of the investigation on human sculls discovered at Toyama (Shinjuku), Shinjuku ward, 1992. Sakura’s investigation was carried out under the commission by Shinjuku ward.

[16] op.cit

[17] Yuasa Ken, Memory never destroyed, 1981, Nicchu Publishing Co., In this book Yuasa confesses his experiences to conduct surgical training on Chinese to kill.

[18] Tuneishi Kei-ichi, Biological warfare unit which disappeared, 1981, Kaimei-sha

[19] Kitano Masaji, On epidemic hemorrhagic fever, The History of Army Hygiene during the Greater East Asia War, vol. 7, Hygiene School of Self Defense Army, 1969

[20] Ikeda Naeo, Experimental Studies on Epidemic Hemorrhagic Fever: Pediculus Vestimenti and Xenopsylla Cheopis as Suspected Vectors of the Disease, Japanese Journal of Infectious Diseases, 1968, vol.42, No 5, pp.125-130

[21] Yoshimura, Seventy-seven Years in Retrospect

[22] Yoshimura Hisato and Iida Toshiyuki, Studies on the Reactivity of Skin Vessels to Extreme Cold, Japanese Journal of Physiology. Part 1, 1950. Part 2, 1952. Part 3, 1952

[23] Tsuneishi Kei-ichi and Asano Tomizo, Biological warfare unit and two physicians who committed suicide, 1982, Shincho-sha

[24] Naito Ryoichi, Report of Investigation Division, Legal Section, GHQ, SCAP, April 4, 1947

[25] Hill & Victor Report

[26] Ishikawa Tachiomaru, On Plague, Japanese Journal of Pathology, vol.34, No.1 & 2, 1944