26 THE ETIOLOGY OF THE BACTERIAL DISEASES. 



The time will probably come when the true test of the specific 

 character of a germ will be made with the chemical products. A 

 given bacterium may not multiply in the circulating blood of a dog, 

 and failure to do so is by no means proof that the same organism 

 might not cause disease in man ; but every germ which causes dis- 

 ease in man does so by its chemical products ; and if these be isolated 

 and injected into the dog in sufficient quantity a poisonous effect will 

 most likely follow. In the study of the bacteria of the infectious 

 diseases, the third and fourth of Koch's rules have not been com- 

 plied with in many cases, as has been stated, on account of the in- 

 susceptibility of the lower animals. The majority of investigators, 

 meeting with this difficulty, have been inclined to rest content with 

 the first two rules, and to conclude that when a . given germ is con- 

 stantly present in a given disease and not found in other diseases, 

 that it is the cause of the disease with which it is associated. In 

 1889, Vaughan suggested that in those instances in which the third 

 and fourth of Koch's rules cannot be complied with on account ot 

 the insusceptibility of the lower animals, it should be shown that 

 the germ can produce chemical poisons which will induce in the 

 lower animals in an acute form the characteristic symptoms of the 

 disease, before the proof that the given germ is the cause of the dis- 

 ease be accepted as positive. 



The science of bacteriology has of necessity been largely founded 

 upon morphological studies. Bacteriologists have given their time 

 and attention to the discovery of bacterial forms in the diseased 

 organism, and to observations of characteristics in structure and 

 growth of different species of bacterial life. This is perfectly proper, 

 but we must also study the physiology and chemistry of germs and 

 until this is done we must remain ignorant of the true cause of dis- 

 ease, and so long as we remain ignorant of the cause it cannot be 

 expected that we shall discover scientific and successful methods 

 of treatment. Suppose that our knowledge of the yeast plant was 

 limited to its form and method of growth ; of how little practical 

 importance would this knowledge be. That the yeast plant requires 

 a saccharine soil before it can grow, that given such a soil it produces 

 carbonic acid gas and alcohol are the most important and practical 

 facts which have been ascertained in its study. Likewise, the con- 

 ditions under which pathogenic germs multiply, and the products 

 which they elaborate in their multiplication, must be ascertained be- 

 fore their true and complete relationship to disease can be understood. 



In saying that the morphological work upon which the science of 

 bacteriology largely depends is inadequate, we wish that it may be 

 plainly understood that we are not offering any hostile criticisms 

 upon the great men who have done this work and who have formu- 

 lated conclusions therefrom. The development of bacteriology has 

 been in accordance with the natural law governing the growth of all 



