XIII. ] THE BIOLOGICAL SCIENCES AND MEDICINE. 345 



army, not of that of a watch or of a hydraulic apparatus. 

 Of this army each cell is a soldier, an organ a brigade, 

 the central nervous system headquarters and field 

 telegraph, the alimentary and circulatory system the 

 commissariat. Losses are made good by recruits 

 born in camp, and the life of the individual is a 

 campaign, conducted successfully for a number of 

 years, but with certain defeat in the long run, 



The efficacy of an army, at any given moment, 

 depends on the health of the individual soldier, and 

 on the perfection of the machinery by which he is led 

 and brought into action at the proper time; and, 

 therefore, if the analogy holds good, there can be 

 only two kinds of diseases, the one dependent on 

 abnormal states of the physiological units, the other 

 on perturbations of their co-ordinating and alimenta- 

 tive machinery. 



Hence, the establishment of the cell theory, in 

 normal biology, was swiftly followed by a " cellular 

 pathology," as its logical counterpart. I need not 

 remind you how great an instrument of investigation 

 this doctrine has proved in the hands of the man of 

 genius to whom its development is due, and who 

 would probably be the last to forget that abnormal 

 conditions of the co - ordinative and distributive 

 machinery of the body are no less important factors 

 of disease. 



Henceforward, as it appears to me, the connection 

 of medicine with the biological sciences is clearly 

 defined. Pure pathology is that branch of biology 

 which defines the particular perturbation of cell-life, 



