210 W. II. BLOOK 



probable intermediate stage between carbohydrate and fatty acid, pyruvic 

 acid CIL,.CO.COOH, which she lias shown to produce straight chain 

 higher fatty acids in vitro by condensation with fatty aldehyds. To get 

 around her own objection that aldehyds are not found in living organisms 

 she postulates that combination is affected with aldehyds in the "nascent" 

 condition. The earlier suggestion of Emil Fischer that the higher fatty 

 acids are formed by direct condensation of sugar molecules with reduction 

 and oxidation has neither chemical nor biological evidence to support it, 

 but is nevertheless interesting since the most widely distributed fatty 

 acids, steari.c, olcic, linoleic, etc., are those containing eighteen carbon 

 atoms in the chain, while the sugar most commonly present is a hexose. 

 It seems likely that the higher fatty acids may be synthesized in more 

 than one way and that the intermediate ones may be formed either by 

 synthesis from the lower ones and the elementary substances or by de- 

 gradation from the higher members. 



Fat Excretion 



Probably no one of the foodstuffs is completely burned in the animal 

 organism. The occurrence in the urine of residues of the protein molecule 

 which still have some calorie value urea, uric acid, traces of aniino 

 acids, etc. is well known. The much debated question of the presence 

 of sugar in normal urine has recently been convincingly answered in the 

 affirmative by Benedict. Traces of fatty acids are present in normal 

 urine but except in rare conditions the amounts found are not impor- 

 tant Fatty material, mainly in the form of fatty acids, is always 

 present in the feces in considerable amounts. This fat may come from 

 at least three sources: (a) undigested material from the food, (b) from 

 the cellular material of the gastro-intestinal tract epithelial cells, bodies 

 of bacteria, etc., and (c) a true excretion of unused or unusable fat. To 

 what, extent food fat passes the tract unabsorhed under normal conditions 

 cannot be stated, but it seems likely from considerations discussed earlier 

 in the chapter that fats suitable as regards consistency and composition 

 are completely digested and absorbed. Some of the feces fat undoubtedly 

 arises from cellular material, -but there is also considerable evidence to 

 show that there is a true excretion of fat into the intestine. In fasting, 

 fat is present in the feces to the extent of about % of the total dry matter. 

 Isolated rings of intestine with their blood supply intact fill up with 

 material similar to feces containing about 35 per cent of their content of 

 fat, an amount, when calculated for the whole intestine, agreeing with 

 the figure for fat in fasting feces (Hermann, 1880-00). Loops of intestine 

 with one or both ends opening outside the abdominal wall secrete a fluid 

 which contains fatrv material. In some animals the excretion flows freely 



