152 



Indeed the subject of animal heat, as is well known, never has been 

 and never can be explained by chymical analogies; for the agents of 

 chymistry, though necessary, are rather of a secondary and subordi- 

 nate kind. Not but that chymical changes and processes must 

 happen in the performance of the function we are considering, but 

 the true ones remain to be investigated, and require that the more 

 essential agencies should be taken into the account. Blood, in 

 parting with the principles which are required or compelled by the 

 other properties of life, cannot in this way yield heat ; or extraneous 

 heat would be unnecessary to begin processes of life, in a body 

 which possesses within itself a capacity to produce it. 



20. There is also another point of analogy between the 

 functions of calorification in animals and vital assimilation: they are 

 each supportable only by arterial blood. Here again we are re- 

 minded of the elementary sources: blood made from food, food 

 from earth; arterial blood, made by food and air; arterial blood 

 supporting life and heat, or we may say only life, as heat is an 

 essential or constituent part of the common forms of life; arterial 

 blood, having supported life and heat, has lost its elements, or at 

 least those from air, and becoming venous blood, requires a new 

 constitution to become again the supporter of the organic spirit. 

 Some further considerations connected with this topic will fall under 

 the titles of " preparatory functions, blood, &c." What is here 

 said will not be properly estimated unless it is connected with every 

 peculiar view of relations before expressed. 



