42 SCIENTIFIC FEEDING OF ANIMALS 



it into the animal body, and that is in the food. 

 It is, in fact, an essential condition of life that heat 

 and energy should be generated in the body itself, 

 and it is in the living cells of the organism that 

 they are produced from the digested nutrients 

 which are brought in the blood supply to all parts 

 of the body, and there taken up by the cells. 

 Heat and energy, then, are only generated in the 

 animal body by the decomposition and combustion 

 of organic materials which the cells have received 

 from the blood. The combustion is preceded as a 

 rule by a splitting up of the compounds, probably 

 under the influence of enzymes. Simpler substances 

 are obtained in this way, and they are oxidised by 

 means of the oxygen in the blood. The fine blood- 

 vessels of the lungs take up the oxygen, which is 

 drawn in with each breath of air, and transport it 

 in the blood through the whole body. 



Whenever energy or heat are to be generated this 

 oxygen unites with the substances which have been 

 prepared for the combination by a preliminary 

 cleavage. The nitrogen-free substances — such as 

 carbohydrates, fats, and organic acids — yield there- 

 by carbon dioxide and water, which are the same 

 products as those formed when ordinary combustion 

 takes place outside the body. 



In a similar manner to that by which oxygen is 

 brought to the cells, but in the opposite sense, the 

 carbon dioxide is dissolved in the blood, reaches 



