20 BACTEBIOLOQY. 



origin of many obscure diseases. So universal became 

 the belief in a causal relation between these " animal- 

 cules " and disease that it amounted almost to a germ- 

 mania. It became the fashion to suspect the presence 

 of these organisms in all forms and kinds of disease, 

 simply because they had been demonstrated in the 

 mouth, intestinal evacuations, and water. 



Though nothing of value at the time had been done 

 in the way of classification, and still less in separating 

 and identifying the members of this large group, still 

 the foremost men of the day did not hesitate to ascribe 

 to tliem not only the property of producing pathological 

 conditions, but some even went so far as to hold that 

 variations in the symptoms of disease were the result 

 of differences in the behavior of the organisms in the 

 tissues. 



Marcus Antonius Plenciz, a physician of Vienna in 

 1762, declared himself a firm believer in the work of 

 Leeuwenhoek, and based the doctrine which he taught 

 upon the discoveries of the Dutch observer and upon 

 observations of a confirmatory nature which he himself 

 had made. The doctrine of Plenciz assumed a causal 

 relation between the micro-organisms discovered and 

 described by Leeuwenhoek and all infectious diseases. 

 He claimed that the material of infection could be noth- 

 ing else than a living substance, and endeavored on 

 these grounds to explain the variations in the period of 

 incubation of the different infectious diseases. He like- 

 wise believed the living contagium to be capable of 

 multiplication within the body, and spoke of the possi- 

 bility of its transmission through the air. He claimed 

 a special germ for each disease, holding that just as from 

 a given cereal only one kind of grain can grow, so by 



