16 BACTERIOLOGY. 



and identifying the members of this large group, still, 

 the foremost men of the day did not hesitate to ascribe 

 to them not only the property of producing disease con- 

 ditions, but some even went so far as to hold that varia- 

 tions in the appearance of 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, expressed 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 him- 

 self had made. The doctrine of Plenciz assumed a 

 causal relation between the microorganisms discovered 

 and described by Leeuwenhoek and all infectious dis- 

 eases. He claimed that infection could be nothing else 

 than a living substance, and endeavored on these grounds 

 to explain the variations in the period of incubation for 

 the different infectious diseases. He likewise believed 

 the living contagium. to be capable of multiplication 

 within the body, and spoke of the possibility 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 the special 

 germ for each disease ouly that disease can be produced. 



He found in all decomposing matters innumerable 

 minute " animalculse," and was so firmly convinced of 

 their etiological relation to the process that he formu- 

 lated the law : that decomposition can only take place 

 when the decomposable material becomes coated with a 

 layer of the organisms, and can proceed only when they 

 increase and multiply. 



However convincing the arguments of Plenciz appear, 



