ETIOLOGY. 19 



infected, but with difterences in degree, as is evidenced by variation 

 in symptoms, in the length of time that the infecting agent con- 

 tinues to grow and develop in the body, and in the ultimate result. 

 Every physician who has had experience in the treatment of any of 

 the infectious diseases appreciates the importance of the personal 

 equation in his patients. It is a fact, frequently observed clinically, 

 and capable of experimental demonstration, that privation and ex- 

 haustion not only increase susceptibility to infectious diseases but 

 also heighten mortality from the same. 



That some neurotic affections originate from traumatism, has been 

 abundantly demonstrated ; that some are largely due to malnutrition 

 accompanied by improper metabolism or insufficient elimination, or, 

 in other words, are to some extent autogenous, all believe. With a 

 clear understanding that the above classification does not attempt a 

 sharp and marked differentiation of the causes of disease, we will 

 give our attention to a consideration of the etiology of the infectious 

 diseases, and of the traumatic and autogenous, in so far as these are 

 influenced by infection. 



Recognizing the fact that germs do bear a causal relation to some 

 diseases, the question arises, how do these organisms act? Inas- 

 much as anthrax was the first disease demonstrated to be due to bac- 

 teria, attempts to answer this question have generally been made by 

 reference to the microorganism of this affection, or, in other words, 

 the question is changed so as to read, " In what way does the bacillus 

 anthracis induce the symptoms of this disease and cause death ? " 

 Of the proposed solutions of this problem the following are the most 

 important : 



1. It was suggested by Bollinger that apoplectiform anthrax is 

 due to deoxidation of the blood by the bacilli. These germs are 

 aerobic, and it was thought that they might act by depriving the red 

 blood corpuscles of their oxygen. This theory was rendered more 

 tenable by the resemblance of the symptoms of anthrax to those of 

 carbonic acid poisoning. The most prominent of these symptoms 

 are dyspnoea, cyanosis, convulsions, dilated pupils, subnormal tem- 

 perature, and, in general, the phenomena of asphyxia. Moreover, 

 post-mortem examination reveals conditions similar to those observed 

 after death by deprivation of oxygen ; the veins are distended, the 

 blood is dark and thick, the parenchymatous organs are cyanotic, 

 and the lungs are hyperemic. Apoplectiform anthrax was compared 

 to poisoning with hydrocyanic acid, which was at one time believed 

 to produce fatal results by robbing the blood of its oxygen. 



This theory presupposed a large number of bacilli in the blood, 

 and this accorded with the estimate of Davaine, which placed the 

 number at from eight to ten million in a single drop ; but more ex- 

 tended and careful observation showed that the blood of animals 

 dead from anthrax is often very poor in bacilli. Virchow reported 



