NOKMAL FAT METABOLISM 205 



the plasma and the corpuscles of the same animal is different. In general, 

 the lipoid level in the plasma is higher in the carnivora than in the 

 herbivora, being undoubtedly influenced by the amount of fat habitually 

 present in the diet. There is no such difference between the concentration 

 of the lipoid constituents in the corpuscles of the various species, the 

 tendency being rather to a similarity of composition in all. 



The level of the blood lipoids may be affected by various conditions, 

 the most frequent being alimentary lipemia as discussed above. Other 

 foods than fat apparently do not affect the level, at least not unless the 

 diet is continued for some time. Fasting for short periods may or may 

 not raise the level of the blood lipoids (dogs), depending probably on the 

 nutritional condition of the animal. After the first two weeks of fasting 

 there is generally a slow fall, although here again the nutritional condition 

 of the animal at the beginning of the fast is probably important. Nar- 

 cotics chloroform, ether and alcohol (especially the two latter) if long 

 continued generally cause an increase of the blood lipoids. Chloroform 

 may not produce any effect during or immediately after the narcosis, but 

 the effects may appear two or three days later. As reasons for the effects 

 may be given the increase in the lipoid solvent power of the blood due to 

 the dissolved narcotics and also their poisonous effects on the tissues, 

 especially the fatty tissues which absorb these substances selectively 

 producing more or less disintegration of the cells. Poisoning with phos- 

 phorus or phlorizin will sometimes produce an increase of the blood lipoids, 

 but the reaction is not constant. In late pregnancy in mammals there is 

 often a rise in blood lipoids, due probably to preparation for lactation. 

 It has been found that there is a relation between the level of blood lipoids 

 and the amount of fat secreted in the milk of lactating animals, also that 

 the lipoid phosphorus is higher in lactating animals than in dry ones. 



Fat in the Tissues 



Storing of Fat. Lipoid material exists in the tissues in two states or 

 conditions: (a) stored, or inactive, consisting of almost pure fat with not 

 more than traces of other lipoids ; and (b) cell lipoid, "built in" or active, 

 forming part of the living tissue and taking an active part in life processes. 

 Of this latter, phospholipoid is the one present in largest amount and 

 widest distribution, then cholesterol and its compounds followed by the 

 series of more or less well characterized substances which include most 

 of the known lipoids. The cell lipoids are relatively constant in com- 

 position and appear to be characteristic of the tissue. 



Stored fat is found in various parts of the animal body, mainly in 

 more or less well defined fat depots such as the abdominal, subcutaneous 

 and intermuscular, and around the organs. It is not normally found 



