CENTURY'S PROGRESS IN SCIENTIFiC MEDICINE 



many ; American pork was excluded altogether from 

 France ; and the whole subject thus came prominently to 

 public attention. But important as the trichina parasite 

 proved on its own account in the end, its greatest im- 

 portance, after all, was in the share it played in direct- 

 ing attention at the time of its discovery in 1833 to the 

 subject of microscopic parasites in general. 



The decade that followed that discovery was a time 

 of great activity in the study of microscopic organisms 

 and microscopic tissues, and such men as Ehrenberg and 

 Henle and Bory Saint Yincent and Kolliker and Roki- 

 tansky and Reraak and Dujardin were widening the 

 bounds of knowledge of this new subject with details 

 that cannot be more than referred to here. But the 

 crowning achievement of the period in this direction 

 was the discovery made by the German J. L. Schoen- 

 lein in 1839, that a very common and most distressing 

 disease of the scalp, known as favus, is really due to the 

 presence and growth on the scalp of a vegetable organ- 

 ism of microscopic size. Thus it was made clear that 

 not merely animal but also vegetable organisms of ob- 

 scure, microscopic species have causal relations to the 

 diseases with which mankind is afflicted. This knowl- 

 edge of the parasites was another long step in the direc- 

 tion of scientific medical knowledge; but the heights to 

 which this knowledge led were not to be scaled, or even 

 recognized, until another generation of workers had en- 

 tered the field. 



in 



Meantime, in quite another field of medicine, events 

 were developing which led presently to a revelation of 

 greater immediate importance to humanity than any 



365 



