OF VITAL MOTION. 43 



and it would seem that the chief difference between 

 this process and that of decay consists partly in the 

 degree of this resistance, and partly in the destruction 

 being masked in the one case by the repairs of nutri- 

 tion. There is no difference in the essential nature 

 and products of the acts, but simply in the conditions 

 in which they take place in the economy. 



Viewed in this relation, the force connected with 

 the process of respiration must be considered, in great 

 part at least, as physical and mechanical in its cha- 

 racter, for it is difficult to attach the idea of vitality 

 to a change, so closely allied to combustion and putre- 

 factive disorganization : and the more so, as the effects 

 upon the capillaries may be explained by this means. 

 The dilated condition of the vessels, when the function 

 of respiration is vigorous, may be regarded indeed as 

 the natural consequence of the free extrication of heat, 

 which must take place under these circumstances, and 

 the shrunk and contracted condition when the process 

 flags, as an equally necessary consequence of the 

 diminished supply of the same agent.* 



* The function of respiration, allied as it is to the processes of 

 decay and combustion, is essentially destructive to the organism; 

 and if certain circumstances did not exist, by which it was kept 

 within bounds, the body would soon kindle up into fever or 

 actual flame. The distinctive gaseous product, moreover, is 

 highly poisonous in its character, and hence a second reason why 

 the function would be inimical to the wellbeing of the creature 

 unless properly restrained and checked. It may be interesting, 



