NUTRITION 277 



to be formed by the liver from ethyl alcohol through the intermediate stage 

 of acetaldehyde ; so that acetaldehyde is, as it were, the meeting place of two 

 reactions, both leading to aceto-acetic acid, the one from pyruvic acid, the other 

 from ethyl alcohol. 



The further oxidation of aldehyde to carbon dioxide and water is probably 

 through acetic acid, as suggested by Neubauer's change of pyruvic into acetic 

 acid in the organism. This would then be the chief reaction ; those leading to 

 alcohol or to aceto-acetic acid diverging at the acetaldehyde stage. 



Another mode of oxidation of glucose should be referred to, namely, that to glucuronic acid, 

 in which the CH.,OH group of glucose is converted into COOH. Further stages of oxidation 

 would yield saccharic and oxalic acids. Camphor, administered to an animal, is excreted in 

 combination with glucuronic acid (Musculus and von Mering, 1875). That this acid arises 

 from oxidation of glucose is shown by the experiments of Paul Mayer (1902), who found that, 

 in inanition, in which very little glycogen remains stored up, scarcely any glucuronic acid 

 was excreted on administration of camphor ; whereas, if glucose was administered at the same 

 time, the usual amount was obtained. It is doubtful whether, normally, further oxidation 

 takes place along this path, siace oxalic acid is only oxidised with great difficulty in the 

 organism (Dakin, 1912, p. 45). At any rate, this mode of oxidation of glucose is not the 

 chief or normal one. 



Diabetes. If the pancreas be removed, and in some pathological conditions, 

 large quantities of glucose are excreted by the kidneys. A remarkable fact is 

 that, even after all carbohydrate stores are used up and none is given in the 

 food, the organism breaks down body-protein in order to form glucose. From 

 the experiments of Cathcart (page 269 above) we have seen the necessity of 

 carbohydrate for protein synthesis and the facts of diabetes suggest that the 

 cells imperatively demand carbohydrate. It is interesting to note that, even 

 after a prolonged fast, sugar is never absent from the blood of the normal animal. 



The experiments of Lusk (1910) have shown that glycine, alanine and three of the carbon 

 atoms in aspartic and glutamic acids are converted into glucose in the organism and that 

 100 parts of meat can give 58 parts of glucose. Since the reaction is, doubtless, reversible, 

 the possibility of production of various amino-acids from glucose is shown. For further 

 information on the question of diabetes see Starling's "Textbook" (1912, pp ; 903-914). 



THE FUNCTION OF CANE-SUGAR IN THE PLANT 



According to Parkin (1911), saccharose is the sugar of most importance in 

 the plant, both as reserve carbohydrate and as circulating sugar. It serves, in 

 fact, as regards carbohydrate, much the same purpose as asparagine in respect 

 of protein metabolism (Horace T. Brown, 1906). Saccharose has properties that 

 fit it especially for such purposes. It is very soluble and yet easily crystallises. 

 It is easily hydrolysed by acids and by invertase. It- has no reducing properties, 

 since the aldehyde group is not functional. It appears that it can be condensed 

 to starch, without previous hydrolysis, and probably also to cellulose. 



THE METABOLISM OF FAT 



The fats taken as food, or found in various situations in the body of the 

 organism, are the tri-glycerides of the higher fatty acids, sometimes accompanied, 

 as in milk, by small amounts of the glycerides of the lower fatty acids, butyric, 

 caproic, etc. The acid may be either a saturated one, as stearic, or an unsatu rated 

 one, such as oleic, in which there are carbon atoms united by double bonds 

 ("ethylene linkage"). 



The substances known as "lipoids," which were described above (page 130), 

 are also found in the tissues. The function of these in the formation of the cell 

 membrane has also been discussed. 



FORMATION OP FAT IN THE ORGANISM 



1. From Fat in the Food. If not oxidised for energy needs, fats taken as food 

 appear to be deposited in the tissues without change. Lebedev (1882) fed dogs, 

 which had lost the greater part of their fat from inanition, either on a diet 

 containing mutton fat in considerable amount, or on a similar diet containing 

 linseed oil in place of the mutton fat. After some weeks, it was found that the 



