GRADUATES IN MEDICINE. 325 



principles have been ascertained. The principles of your pro- 

 fession are derived from the study of life and its conditions. 

 Herein consists the chief difficulty with which medicine has 

 had to contend. The very circumstance that vitality is sub- 

 ject to disturbance in direct proportion to the comprehensive- 

 ness of the conditions under which it is maintained, involves 

 its study in complexities of a kind which do not oppose the 

 advance of the science of inorganic nature. Vitality can 

 only be investigated as it is manifested in individual organisms. 

 Now, although the organisation of the individual is a perfect 

 system in itself, it is not the less a system dependent on con- 

 ditions external to itself. All its parts and actions are pre- 

 arranged in reference to as much of what is external to it as 

 its conditions of existence involve. It can live or subsist in 

 any locality in which these conditions are provided for it. If, 

 again, these conditions are in any way transgressed, or if they 

 are withheld, a diminution of health, or the access of disease, 

 or of death, necessarily supervenes. As with the individual 

 so with the species, the existence and health of which depend 

 at any given time on the presence and integrity of the con- 

 ditions of its collective vitality. The localisation of all the 

 various species, genera, families, and orders, of organised 

 beings in space, and their existence or non-existence in time, 

 are referable to this fundamental law of organisation. From 

 this law also is derived what appears to be a general principle 

 in medicine — that diminution of health, and the existence of 

 disease, arc the direct results of the disturbance or removal 

 of one <ir more <>/' the conditions of health, so that the whole 

 extended subject of the phenomena, nature, and causes of 



pecial di ea es and injuries resolves itself into the investiga 

 ii"H of the immediate or more or Less remote disturbances of 

 the conditions of health. 



A second general principle in medicine follows from what 

 has now been staid I. For it appears that the removal oj 



