CHAPTER III 



THE UTILISATION OF DIGESTED NUTRIENTS 

 IN THE ANIMAL BODY 



(i) General considerations. 



THE body temperature of a living, warm- 

 blooded animal lies between 37-40 C. (99- 

 104 F.), and so, as a rule, is higher than the 

 temperature of the surrounding atmosphere. On 

 this account animals are continually losing heat, 

 and must have some source from which the loss 

 can be made good. 



The movements which take place during respira- 

 tion, the work performed by the heart, the changes 

 in shape of the digestive organs, the movements of 

 the voluntary and involuntary muscles, etc., all 

 use up energy, which must be replaced if life is to 

 continue. It is impossible to prevent the loss of 

 animal heat, as will be seen later (Chap. IV), even 

 if the surrounding temperature is raised. The 

 same holds good, also, in the case of dissipation of 

 energy. Energy can be brought into a machine in 

 various ways, but there is only one way of bringing 



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