TO BE DUE TO SPECIFIC MICROORGANISMS. 529 



destroyed by a correspondingly low temperature and by the action of vari- 

 ous chemical disinfectants. 



YELLOW FEVER. 



In the writer's ' ' Report upon the Prevention of Yellow Fever by Inocu- 

 lation," submitted in March, 1888, the following conclusions are given as 

 the result of his investigations at the date of this report : 



Conclusions. 



Facts relating to the endemic and epidemic prevalence of yellow fever, 

 considered in connection with the present state of knowledge concerning the 

 etiology of other infectious diseases, justify the belief that yellow fever is 

 due to a living microorganism capable of development under favorable local 

 and meteorological conditions external to the human body, and of establish- 

 ing new centres of infection when transported to distant localities. 



Inasmuch as a single attack of yellow fever, however mild, protects, as a 

 rule, from future attacks, there is reason to hope that similar protection would 

 result if a method could be discovered of inducing a mild attack of the dis- 

 ease by inoculation or otherwise. 



The hypothetical yellow-fever germ, multiplying external to the human 

 body in unsanitary places in tropical regions where the disease is endemic, 

 or during the summer months in the area of ics occasional epidemic preva- 

 lence, establishes infected localities, and susceptible persons contract yellow 

 fever by exposure in these infected areas. We infer, therefore, a priori, 

 that the yellow-fever germ invades the system by the respiratory tract, by 

 the alimentary canal, or from the general surface of the body, and it should 

 be found in the blood and tissues, or in the alimentary canal, or upon the 

 surface. 



Another possibility presents itself, viz. , that the germ multiplying in un- 

 sanitary localities external to the body produces a volatile poison which 

 contaminates the air, and that an attack is induced by the toxic effects of 

 this potent chemical poison. The more or less prolonged period of incuba- 

 tion two to five days in numerous cases in which the attack has been de- 

 veloped after removal from the infected locality, is opposed to this latter 

 hypothesis. 



In the light of what is known of the etiology of other infectious dis- 

 eases, the hypothesis that the germ really finds entrance to the body of 

 the person attacked and multiplies within it is that which presents itself as 

 most probable, and it hardly seems worth while to consider any other, un- 

 less this is proved by a complete investigation not to be true. 



Naturally the attention of investigators has first been given to a search 

 for the " germ " in the blood of those attacked and in the blood and tissues 

 of the victims of the malady. 



The researches made up to the present time have failed to demonstrate 

 the constant presence of any microorganism in the blood and tissues of 

 those attacked. 



My own researches, recorded in the foregoing report, show that no such 

 microorganism as Dr. Domingos Freire, of Brazil, has described in his pub- 

 lished works, or as he presented to me as his yellow-fever germ at the time 

 of my visit to Brazil, is found, as he asserts, in the blood and tissues of 

 typical cases of yellow fever. There is no satisfactory evidence that the 

 method of inoculation practised by Dr. Domingos Freire has any prophy- 

 lactic value. 



The claims of Dr. Carmona y Valle, of Mexico, to have discovered the 

 specific cause of yellow fever have likewise no scientific basis, and he has 

 failed to demonstrate the protective value of his proposed method of pro- 

 phylaxis. 



It is highly important, in the interest of science and of the public health, 

 that further investigations be made by more exact methods which have 



