LACTIC ACID. 377 



the occurrence of coagulation, and protoplasmatic activity here 

 manifestly does not enter into consideration. We are hence forced 

 to the conclusion that the formation of lactic acid is either referable 

 to the action of a ferment which is destroyed by chloroform, or that 

 it results from a spontaneous decomposition of certain substances 

 which are especially unstable. 



Besides paralactic acid, traces of common lactic acid also are said 

 to occur in muscle-tissue. To isolate the bodies in question, the fol- 

 lowing procedure may be employed. 



Isolation and Quantitative" Estimation. A carefully weighed 

 amount of muscle-tissue is finely hashed, repeatedly extracted with 

 cold water, and the mixture passed through a muslin filter. The 

 resulting fluid is feebly acidified with sulphuric acid and boiled, 

 so as to remove the coagulable albumins. Baryta-water is now 

 added so long as a precipitate is formed ; this is filtered off. The 

 filtrate is freed from the barium that was added in excess by pass- 

 ing carbon dioxide into the solution, when it is boiled, filtered, and 

 concentrated to a thin syrup. Care should be taken, however, that 

 the temperature does not exceed 70 C. toward the end. The re- 

 sulting material is treated with ten times its volume of absolute 

 alcohol, set aside for a while, and filtered. The alcoholic solution is 

 evaporated on a water-bath, and the remaining thick syrup treated 

 with about an equal amount of a moderately dilute solution of phos* 

 phoric acid. This liberates the lactic acid from its salts, while the 

 chlorides and sulphates remain unaffected. The lactic acid is then 

 extracted with ether. The ether is distilled off, the residue boiled 

 with water and an excess of carbonate of zinc, and filtered while still 

 hot. The filtrate is concentrated to a small volume, when on stand- 

 ing, and especially after the addition of a small amount of alcohol, 

 the zinc lactate crystallizes out. To separate the paralactate from 

 the common lactate, which, as I have said, is also found in traces in 

 the muscle-tissue, the crystals are placed in absolute alcohol, which 

 dissolves the paralactate (solubility 1 : 1100), while the common form 

 is insoluble. They are then finally dried and weighed. 



To obtain the lactic acid as such the lactates are decomposed with 

 hydrogen sulphide. The resulting zinc sulphide is filtered off, 

 washed with water, when filtrate and washings are evaporated at 

 70 C. to a small volume. 



Both acids are amorphous, and are obtained in the form of a thick 

 syrup, which is soluble in water, alcohol, and ether. Of their salts, 

 the zinc salts are especially characteristic and serve to distinguish 

 the two forms from each other. As I have indicated, the common 

 lactate is insoluble in absolute alcohol. It crystallizes with three 

 molecules of water, which escape at a temperature of 105 C., so 

 that the loss of weight will then correspond to 18.18 per cent. The 

 paralactate, on the other hand, is soluble in absolute alcohol, though 

 with difficulty, and crystallizes out with only two molecules of water, 

 which likewise escapes at 105 C. In this case the loss of weight 

 amounts to 12 per cent. Both the free acid and the paralactate are 



