XIV BIOLOGICAL SCIENCES AND MEDICINE 369 



fluid possessed of a " vis essentialis " and a 

 " solidescibilitas " ; or, in modern phrase, as 

 protoplasm susceptible of structural metamorphosis 

 and functional metabolism: and that the only 

 machinery, in the precise sense in which the 

 Cartesian school understood mechanism, is, that 

 which co-ordinates and regulates these physio- 

 logical units into an organic whole. 



In fact, the body is a machine of the nature 

 of an 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 ali- 

 mentary 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 physiologi- 

 cal units, the other on perturbations of their 

 co-ordinating and alimentative 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 investiga- 



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