The History of the Subject 27 



In 1911 Noguchi succeeded in obtaining pure cultures of 

 the treponema. 



During the time that so much investigation of the prob- 

 lems of infection was in progress the discoveries were by no 

 means restricted to the- bacteria and their products, as the 

 reader might infer from the perusal of a chapter whose pur- 

 pose is to explain the development of the department of 

 science now known as Bacteriology. Other organisms of 

 different i. e., animal nature were also found in large 

 numbers. 



In 1875 Losch discovered the Amoeba coli; in 1878 Rivolta 

 described the Coccidium cuniculi of the rabbit; in 1879 

 Lewis first saw Trypanosoma lewisi in the blood of the rat; 

 in 1 88 1 Laveran discovered Plasmodium malariae in the blood 

 of cases of human paludism; in 1885 Blanchard described 

 the sarcocystis in muscle-fibers; in 1893 Councilman and 

 Lafleur studied Amoeba dysenteriae in the stools and tissues 

 of human dysentery; in 1903 Leishman and Donovan found 

 the little body Leishmania donovani in the splenic juice of 

 cases of kala-azar, and in 1903 Dutton and Forde, working 

 independently, observed trypanosomes the Trypanosoma 

 gambienseof African lethargy in the blood of human beings. 



Each of these was followed by new discoveries and addi- 

 tions in its own sphere, and the systematic consideration of 

 these protozoan organisms can only be undertaken in a text- 

 book devoted to animal parasites. 



Many of these organisms, however, can be cultivated and 

 studied by the methods of bacteriology, and, indeed, it is the 

 progress of bacteriology that has made our ever-increasing 

 knowledge of them possible. 



That the specific micro-organisms of many of the infectious 

 diseases remained undiscovered was a source of perplexity 

 so long as it was supposed that all living things must be visible 

 to the eye aided by the microscope. To-day, thanks to the 

 invention of the ultramicroscope, that shows the existence 

 of things too small to be defined, and still more to the adap- 

 tation of the method of filtration to the study of the diseases in 

 question, we realize that the " viruses " of disease may be vis- 

 ible or invisible and that they have no limitations of size. 

 Just as bacteria readily find their way through paper filters, 

 so the invisible and hence undescribed viruses i. e., micro- 

 organisms of rabies, poliomyelitis, yellow fever, pleuro- 

 pneumonia of cattle, foot-and-mouth disease, rinderpest, 



