ANIMAL COMPOUNDS 319 



Pressure caused by blood plasma being forced out of the 

 capillaries, possibly contraction of lymph vessels, and par- 

 ticularly muscular exercise, all serve to force lymph along 

 its vessels so that a continuous stream is poured into the 

 veins from the thoracic duct. 



Lymph being essentially blood plasma is a clear to opales- 

 cent liquid, slightly alkaline in character, containing proteins, 

 dextrose, sodium chloride and carbonate, some other salts, 

 white corpuscles, and a small amount of fibrinogen. It 

 also contains oxygen and carbon dioxide dissolved in it, 

 although part of the latter is combined with sodium car- 

 bonate. The proportion of the various constituents is not 

 quite the same as that in blood plasma and varies from 

 one part of the body to another according to the needs of 

 the body. 



233. Animal Compounds. — Many of the animal compounds 

 are the same as those in plants, but there are some differences, 

 enough to warrant a brief review of the subject. In this 

 discussion, of course, no attention is paid to compounds 

 eaten by the animal for food— only those compounds 

 actually absorbed and utilized by the animal. For conveni- 

 ence in comparison, the same order will be observed as in 

 Chapter III on Plant Compounds. 



(a) Carbohydrates. — Of the many carbohydrates known 

 only three are of importance in the animal. 



1. Dextrose, already described, Section 52. It is found in 

 blood, liver, muscles, and other tissues, serving as a source of 

 energy by its oxidation, and also as a source of fat (Section 

 239, a). 



2. Glycogen, Animal Starch (CeHifAOn. — It is a white, 

 amorphous, tasteless powder, dissolving in water to an 

 opalescent solution, and giving a dark red color with iodine. 

 On hydrolysis with mineral acids or with amylolytic enzymes 

 it yields dextrose. The liver is the principal repository of 

 glycogen, containing from 1 to 4 per cent. The liver produces 

 glycogen from dextrose, levulose, and probably galactose, 

 the form of soluble carbohydrates absorbed. As needed by 

 the body the liver reproduces dextrose. Glycogen is also 

 found in the muscles to a maximum extent of 1 per cent. 



