162 ELEMENTARY AGEICULTURAL CHEMISTRY 



conveyed to the tissues, while another portion is stored in 

 the liver in the form of glycogen, CellioOs, an amorphous white 

 powder occurring in the liver to the extant of from very little 

 or none in starvation to 10 or 12 per cent, under a rich carbo- 

 hydrate diet. 



Only a small portion of the fat is saponified (2.6., decomposed 

 into glycerol and fatty acids), the greater portion being merely 

 emulsified by the action of the pancreatic fluid and the bile. 

 The minute globules of fat apparently pass through the walls of 

 the intestines into the lacteals, and thus into the blood. The 

 proteids are chiefly absorbed as peptones and albumoses, 

 though apparently they are transformed back into proteids in 

 the act of absorption, for no peptones can be found in the 

 blood. 



According to recent researches proteids are hydrolysed by 

 the digestive juices into amino-acids, and in this form enter 

 the blood stream. The amino-acids are then used by the 

 animal in building up the proteids required in its tissues. 

 Unless all the amino-acids necessary for forming animal 

 proteids are present in sufficient quantities in the proteids of 

 the food proper nutrition cannot occur. In the case of the 

 proteids of certain food-stufFs — e.g., of maize — all the neces- 

 sary amino-acids are not present, and such food-stuflfs cannot, 

 of themselves, support life for long. The subject is at present 

 receiving much attention from biological chemists, and, in 

 the near future, much new light will doubtless be thrown 

 upon it. 



The digestion of the food thus commences in the mouth 

 and is completed in the stomach and intestines, while the 

 digested materials are absorbed by the lacteals and poured 

 into the blood stream from which they are extracted in the 

 building up of tissue. 



The carbohydrates and fats which are oxidised in keeping up 

 the animal heat or in furnishing energy, are exhaled as carbon 

 dioxide and water from the blood in the lungs, while the 

 nitrogenous waste products of the breaking down of muscle, 



