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 

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

 variations in the appearance of 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 re- 

 lation between the micro-organisms discovered and de- 

 scribed by Leeuwenhoek and all infectious diseases. He 

 claimed that the material of infection could be nothing 

 else than a living substance, and endeavored on these 

 grounds to explain the variations in the period of incuba- 

 tion of the different infectious diseases. He likewise 

 believed the living contagium to be capable of multipli- 

 cation 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 only that disease can be pro- 

 duced. 



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. 



