io6 THE CHEMISTRY OF THE TISSUES AND ORGANS. 



per cent, more of the total fat obtainable ; without such preliminary 

 digestion, extraction with ether is useless for quantitative purposes. E. 

 Bogdanow x believes that the fat which is thus soluble in ether with 

 difficulty is a real constituent of the muscle plasma, and states that it is 

 richer in volatile fatty acids than that from the surrounding connective 

 tissues. For " Adipocere," see p. 20. 



Lactic acids. Among the oxypropionic acids with the empirical 

 formula C 3 H 6 3 , one called hydracrylic acid, or ethylene lactic acid, CH 2 

 (OH).CH 2 .COOH, is not found in the body. Small quantities of this 

 material were formerly described 2 as occurring in muscle extracts, but 

 this is not the case ; the acid mistaken for it was acetyl-lactic acid 

 H 3 CH(C 2 H 3 2 )COOH. 3 



The remaining lactic acids^ are stereochemical isomerides of 

 ethylidene lactic acid. They are three in number, and differ in optical 

 activity, and in the solubility, optical activity, and amount of crystallisa- 

 tion water in their zinc, calcium, and lithium salts. 4 



Their formula is CH 3 .CH(OH).COOH. The differences between 

 them are due, according to the theory of Bel and Van't Hoff, and as the 

 expression stereochemical implies, to the space relationships of the atoms. 



The three isomerides are 



(a) The optically inactive acid. This is the ordinary fermentation 

 lactic acid, which occurs in milk when it turns sour ; it has been found 

 in small quantities in muscle, 5 in the grey matter of the brain, 6 and in 

 some cases of diabetic urine. Its most characteristic salts are 



Zinc lactate Zn(C 3 H 5 3 ) 2 4- 3H. 2 ; soluble in fifty-three parts of water 

 at 15 ; in six parts at 100 C. ; almost insoluble in alcohol. 



Calcium lactate, Ca(C 3 H 5 3 ) 2 -h5H 2 ; soluble in 9 '5 of cold, and in 

 all proportions in boiling water. Insoluble in cold alcohol. 



(&) Dextrorotatory lactic acid. This is paralactic, or sarcolactic 

 acid. This is the lactic acid par excellence of muscle. 7 It is found in 

 the blood, 8 particularly after muscular activity. 9 It is found in the 

 urine after muscular activity, 10 during diminution of oxidation processes, 11 

 in phosphorus poisoning, and after extirpation of the liver. 12 It is found 

 as noted when we considered them, in many organs and tissues after 

 death. Its best known salts are 



Zinc sarcolactate, Zn(C 3 H 5 3 ) 2 + 2H 2 0. Soluble in 17 '5 parts of water at 

 15 C., and in 96'4 parts of boiling 98 per cent, alcohol. 



l Arch.f. d. ges. Physiol., Bonn, Bd. Ixv. S. 81. 



2 Wislicenus, Ann. d. Chem. Leipzig, 1873, Bd. clxvii. S. 302. 



3 Siegfried, Ber. d. deutsch. cliem. Gesellsch., Berlin, 1889, S. 2711. 



4 On lithium lactates, see Hoppe-Seyler and Araki, Ztschr. f. physiol. Chem., Strassburg, 

 1895, Bd. xx. S. 365. 



5 Heintz, Ann. d. Chem., Leipzig, 1871, Bd. clvii. S. 314. 



6 Gschleidlen, Arch. f. d. ges. Physiol., Bonn, 1873-4, Bd. viii. S. 71. 



7 Liebig, Ann. d. Chem., Leipzig, 1847, Bd. Ixii. S. 326 ; Wislicenus, ibid., S. 302. 



8 Gaglio, Arch. f. Physiol., Leipzig, 1886, S. 400; Irisawa, Ztschr. f. physiol. Chem., 

 Strassburg, Bel. xvii. S. 340. 



9 Spiro, Ztschr. f. physiol. Chem., Strassburg, 1877, Bd. i. S. Ill : v. Frey, Arch. /. 

 Physiol., Leipzig, 1885, S. 557. 



10 Colasanti and Moscatelli, Jahresb. it. d. Fortschr. d. Thicr-Chem., Wiesbaden, 1887, 

 S. 212 ; Marcus, Arch. f. d. ges. Physiol., Bonn, 1886, Bd. xxxix. S. 425. 



11 Araki, Ztschr. f. physiol. Chem., Strassburg, Bde. xv., xvi., xvii., and xix. 



12 Minkowski, Centralbl.f. d. med. Wissensch., Berlin, 1885, No. 2 ; Arch.f. exper. Path. 

 u. Pharmakol., Leipzig, 1886, Bd. xxi. S. 40 ; Marcuse, loc. cit.; Nebelthan, Ztschr. f. Biol., 

 Mimchen, 1889, Bd. xxv. S. 123. 



