THE CELL-DOCTRINE 149 



a mechanistic explanation of vital phenomena. For what- 

 ever one may think of the relative merits of vitalistic and 

 mechanistic concepts of the life-process, the history of biolog- 

 ical science shows that the forward steps have usually con- 

 sisted of further extensions of chemico-physical, and hence of 

 mechanistic, explanations. 



This development within the science of physiology 

 exerted a profound influence upon the progress of medicine. 

 The theory of cells led to medical advances which were un- 

 thought of at an earlier period. We find here the most 

 advanced phase in that control of nature, which may distin- 

 guish biological science in the future. During recent years 

 the physiologists have laid the foundations for changes in 

 medicinal science as far-reaching as those necessitated by 

 the germ-theory of disease. Their studies in nutrition, in 

 secretion, in the chemistry of blood and tissue, and the like 

 are restricting the art of medicine and forcing progress along 

 the lines of science. These investigations could never have 

 reached their present state in the absence of some com- 

 prehensive theory of microscopic organization. 11 



The theory that certain diseases are caused by minute 

 organisms or germs, living as parasites within the bodies of 

 animals and plants, has been intimately associated with the 

 theory of cells. Analogies between the spread of disease and 

 the multiplication of living organisms were long recognized, 

 without being explained. For centuries, a variety of dis- 

 orders were attributed to parasitic worms, although the 

 life-cycles of forms like tapeworms were not ascertained 

 until the middle of the nineteenth century. Minute para- 

 sites had, however, been observed within the bodies of 

 larger animals since the early days of the microscope The 

 finding of bacteria in association with particular diseases 

 was, therefore, a suspicious circumstance. The Germ-Theory 

 of disease was established, in correlation with the cell-theory, 

 during the third quarter of the nineteenth century. 



11 Cf. Lee, F. S., "Scientific Features of Modern Medicine." 



