THE BIOLOGICAT SCIENCES AND MEDICINE. 353 



unquestionably largely true. But it is also true, that 

 the living body is a synthesis of innumerable physio- 

 logical elements, each of which may nearly be described, 

 in "Wolffs words, as a fluid possessed of a " vis esssen- 

 tialis," and a " solidescibilitas " ; or, in modern phrase, 

 as protoplasm susceptible of structural metamorphosis 

 and functional metabolism: and that the only machin- 

 ery, in the precise sense in which the Cartesian school 

 understood mechanism, is, that which co-ordinates and 

 regulates these physiological 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 appa- 

 ratus. 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 cam- 

 paign, conducted successfully for a number of years, 

 but with certain defeat in the long run. 



The efficacy of an army, at any given moment, de- 

 pends 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 perturba- 

 tions of their co-ordinating and alimentative machinery. 



Hence, the establishment of the cell theory, in nor- 



