ORGANS OF THE ENERGIZING SYSTEM 83 



etc.), amino-bodies, offensively smelling ptomaines, etc., are 

 formed at the latter end of the bowel. The faeces consist largely 

 of bacteria, undigested food materials, protein fragments, etc. 



Digestion in general. The foodstuffs, bulky in consistency and 

 heterogeneous in constitution, become triturated in the mouth, 

 oesophagus, stomach, etc., and are then subjected to chemical 

 disintegrations by the agencies of enzymes. First their significant 

 constituents — the proteins, fats and carbohydrates, are brought 

 into solution : 



the proteins as peptides, peptones, etc., and finally as amino- 

 acids ; 



the fats as fatty acids and glycerol ; 



the carbohydrates as laevulose, glucose, maltose, galactose, etc., 

 and these reduced products — the amino-acids, the fatty acids, 

 the glycerol and the soluble sugars, are transformed foodstuffs 

 ready to go into circulation. 



29. ON THE ABSORPTION AND CIRCULATION OF THE 

 ELABORATED FOOD MATERIALS 



The heterogeneous contents of the small intestine are called 

 chyme. Simultaneously with the formation of this mixture its 

 absorption begins. The amino-acids and the soluble sugars are 

 directly absorbed, passing through the inner wall of the intestine, 

 and the thin walls of the capillaries, into the blood-stream. The 

 fatty acids and glycerol also pass through the intestinal mucosa, 

 but in so doing they are again combined into neutral fats. The 

 creamy liquid which is called chyle and which is seen, after a meal, 

 in the lymphatic vessels of the intestinal wall consists characterist- 

 ically of minute droplets of neutral, emulsified fats. It goes 

 into the vessel (in man) called the thoracic duct and is finally 

 emptied into the blood-stream. Thus the latter is loaded, after 

 every meal, with the proximate food substances, amino-acids, 

 carbohydrates as sugars and emulsified neutral fats. 



And it is from these substances that the energy-requirements 

 of the animal body are met. Also the growth and repair of tissues 

 are built up upon them. In the reproducing and pregnant 

 animals they supply the materials from which ova and spermatozoa 

 and the embryonic developing tissues are formed. 



2ga. The Circulation, throughout the Body, of the 

 Proximate Food Substances. Generally, in the higher animals, 



