THE CELL-DOCTRINE 153 



diseases have yet to be recognized as such. Nevertheless, 

 what is now the germ-fact stands as the most comprehen- 

 sive generalization within the field of medicine. 



The bearing of the cell-doctrine upon the germ-theory 

 of infectious diseases is obvious. The latter could never 

 have become established without detailed knowledge con- 

 cerning cells. The germ-theory became established along 

 with the fact of cellular continuity between generations. 

 Just as the physical basis of heredity was disclosed in terms 

 of cells, so the physical basis of contagion was found to be 

 the unicellular germ. The one reacted upon the other, 

 although the general theory of cells comprehended the par- 

 ticular theory of germs. It is not putting the case too 

 strongly to say that the cell-theory changed the entire con- 

 cept of the causation of disease, first, through its support 

 of the germ-theory and, second, through its explanation of 

 all pathological functions as abnormal cell activities. Not 

 only were infectious diseases explained, but a clue was 

 furnished for the explanation of all bodily disorders. 



The history of the cell-theory illustrates the origin, de- 

 velopment, and ramification of a fundamental hypothesis. 

 A unifying explanation of innumerable disjointed observa- 

 tions was impossible without proper understanding of mi- 

 croscopic structure. As soon as the cell-theory was pro- 

 mulgated, its value was apparent. The organization of 

 animals and plants, both great and small, was brought 

 within the same category. The clue was discovered, both 

 as regards structure and function, to the origin of the in- 

 dividual, and hence to the continuity between generations. 

 Just as the evolutionary hypothesis unified a multitude of 

 facts regarding visible structures and activities of living 

 things, so the cell-theory unified the phenomena that under- 

 lie the visible features of the body as a whole. With such a 

 theory established, biological science could attack the prob- 

 lems of the living substance with some hope for a successful 

 issue. 



