CHEMICAL BASIS OF THE ANIMAL BODY r . 1233 



importance, as will be seen later on, inasmuch as by their 

 varying solubilities they afford a means of separating the several 

 acids each from the other. 



1. Ethylidene-lactic acid. CH 3 . CH(OH) . COOH. 



This is the ordinary form of the acid, obtained character- 

 istically as the chief product of the lactic fermentation of 

 sugars. 



Lactic acid occurs in the contents of the stomach and intes- 

 tine, more particularly during a diet rich in carbohydrates, and 

 may be readily formed by the digestion of gastric mucous 

 membrane with solutions of dextrose or saccharose. It has been 

 found also in muscles, and according to some observers in the 

 ganglionic cells of the grey substance of the brain. 



The most important salts of this acid are those of zinc and 

 calcium. 



Zinc lactate. Zn (C 3 H 5 3 ) 2 + 3H 2 0. Soluble in 53 parts 

 of water at 15°; in 6 parts at 100°. Almost insoluble in 

 alcohol. 



Calcium lactate. Ca (C g H 5 3 ) 2 + 5H 2 0. Soluble in 9*5 

 parts of cold water ; soluble in all proportions in boiling water. 

 Insoluble in cold alcohol. 



2. Sarcolactic acid. 



This form of the acid is isomeric with the preceding one. 

 In its general chemical behaviour as tested by the various 

 decompositions it can undergo it is found to be identical with 

 ethylidene-lactic acid, the sole observable difference being in 

 the different solubility of its calcium and zinc salts. But both 

 sarcolactic acid and its salts differ strikingly from the preced- 

 ing acid and its salts as regards their physical properties, for 

 the former exert a distinct rotatory action on polarized light 

 while the latter do not. 



This acid has not yet been prepared synthetically and is 

 only known as occurring characteristically in muscles to which 

 it gives their acid reaction, and in blood. In the latter it is 

 found more particularly, as might be expected, after the mus- 

 cles have been in a state of contracting 1 activitv. It is also 

 found in urine, very markedly in case of phosphorus poisoning 

 and in the same excretion after violent muscular exertion, or 

 artificial stimulation of groups of muscles, and very strikingly 

 after extirpation of the liver in birds, and frogs. It is also 

 stated to be formed in variable and slight amount during the 

 lactic fermentation of dextrose. Lactic acid has also been 

 frequently described as a constituent of various pathological 

 fluids ; in these cases it is probable that the acid is often the 

 sarcolactic acid. 



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