The History of the Subject 25 



In the same year, 1905, Castellani discovered the Treponema 

 pertenue, the cause of frambesia or yaws. 



In 1 91 1 Noguchi succeeded in obtaining pure cultures of the 

 treponema. 



In 1913 Flexner and Noguchi appear to have been successful in 

 cultivating the virus of acute anterior poliomyelitis, in vitro. 



During the time that so much investigation of the problems 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 purpose 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 187s Losch discovered the Amoeba coli; in 1878 Rivolta de- 

 scribed the Coccidium cuniculi of the rabbit; in 1879 Lewis first 

 saw Trypanosoma lewisi in the blood of the rat; in 1881 Laveran 

 discovered Plasmodium malarise 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 in- 

 dependently, observed trypanosomes — the Trypanosoma gambiense 

 of African lethargy— in the blood of human beings. 



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 ultra- 

 microscope, that shows the existence of things too small to be 

 defined, and still more to the adaptation of the method of filtration 

 to the study of the diseases in question, we realize that the "viruses" 

 of disease may be visible or invisible and that they have no limita- 

 tions of size. Just as bacteria readily find their way through paper 

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

 organisms — of yellow fever, pleuro-pneumonia of cattle, foot-and- 

 mouth disease, rinderpest, hog-cholera, African horse-fever, infec- 

 tious anemia or swamp sickness of horses, fowl plague, small-pox, 

 cow-pox, sheep-pox, horse-pox, swine-pox, and goat-pox are at some 

 or all stages able to pass through the Berkefeld or diatomaceous 

 earth filters, and some of them through the much less porous unglazed 

 porcelain or Chamberland filters. Thus there is opened a new 

 world that is ultramicroscopic, but still teems with invisible living 

 organisms. 



