8 FOOD INGEST I ON AND ENERGY TRANSFORMATIONS. 



are gathered by harvesters, hunters, or fishermen, brought to the 

 dwelling by transportation agencies, prepared by some member of the 

 household, and finally placed upon the table ready for consumption. 

 With humans the exertion necessary to secure food is no longer indi- 

 vidual, but represents the serious occupation of a large number of 

 persons devoted to this service only. But even after the food has been 

 prepared and placed before the individual, there are certain muscular 

 processes necessary to prepare it for digestion; these are admirably 

 classified by Armsby in the following paragraph: 



"In the process of digestion we are probably safe in assuming that the 

 muscular work of prehension, mastication, deglutition, rumination, peristalsis, 

 etc., constitutes an important source of heat production." 1 



Entirely aside from the external muscular activity incident to the pro- 

 curing and preparing of food and its introduction into the mouth, we 

 have internal processes other than those of mastication, primarily the 

 movements of the stomach and intestinal tract, which may be grouped 

 under the general term of peristalsis. These movements, certainly 

 in ruminants, are very considerable in amount. While with humans 

 rumination does not occur, yet the admirable X-ray observations of 

 Cannon 2 have demonstrated that with men peristalsis is continuous 

 during digestion. How much the movements of peristalsis and seg- 

 mentation contribute to or make demands upon the energy of the body 

 is a problem still to be considered. The possibility of there being 

 extensive demands for these processes in man has been carefully con- 

 sidered by Zuntz and his co-workers. These investigators have been 

 influenced in large part by their observations on ruminants and herbiv- 

 orous animals in general, such animals having a large amount of residue 

 or ballast in the gastro-intestinal tract that must be worked over by the 

 peristaltic movements. 



Finally, a considerable demand is made upon the energy of the body 

 for heat to warm the ingesta. Water and many other fluids are com- 

 monly taken by man at a temperature considerably lower than the 

 temperature of the body ; these must be warmed to body-temperature. 

 Again, certain liquids are taken somewhat above the temperature of 

 the body and therefore may contribute, in part at least, to the heat 

 elimination. The amount of cold ingesta required to be warmed by 

 body heat is invariably much greater than the amount of warm food 

 taken, so that in many instances we have carefully to consider this 

 expenditure of heat. In fact, this has been pointed out as an impor- 

 tant path for the output of heat in diabetics with an enormous excretion 

 of urine. If 3 liters of water are taken and excreted as urine in the 

 course of the day, it will be seen that this water may be warmed from 



'Armsby, The principles of animal nutrition, 2d ed., 1906, p. 374. 

 'Cannon, The mechanical factors of digestion, 1911. 



