96 THE CHEMISTRY OF THE TISSUES AND ORGANS. 



Muscle considered as meat is the most concentrated and most easily 

 assimilable of the animal nitrogenous foods. It forms our chief source 

 of nitrogen. In 100 parts of nitrogen from beef, 774 come from proteid 

 insoluble in water, 10'08 from soluble proteid, and 12'52 from extract- 

 ives. 1 In addition to the proteids, extractives, and salts contained in 

 muscle, the flesh used as food contains a certain variable percentage of 

 fat, even though all visible adipose tissue is cleaned off. In estimating 

 the amount of fat, Dormeyer 2 recommends that the meat should be 

 subjected to artificial digestion before extraction with ether ; ilesh then 

 yields an additional 075 per cent, of fat. 



The following table 3 gives the chief substances in some of the principal 

 meats used as food : 



The flesh of young animals is richer in gelatin than that of old ones; 

 thus 1000 parts of beef yield 6, of veal 50, parts of gelatin (Liebig). 



Meat contains four times the amount of proteid present in an equal 

 weight of milk. 



The process of cooking meat (after it has been kept to allow rigor 

 mortis to pass off) renders the investing connective tissues looser, 

 separates the muscular fibres, and destroys parasitic growths. The 

 muscular fibres themselves, especially if boiled, are rendered more 

 difficult of digestion. 



The muscle plasma and the muscle serum. Kiihne 4 was the first to 

 obtain muscle plasma; he used frogs' muscle. The fresh blood-free 

 muscle is frozen and subjected to strong pressure, the expressed fluid 

 (muscle plasma) is filtered ; it is found to be syrupy in consistence, and 

 faintly alkaline. As the temperature of the plasma rises to that of the 

 air, it clots, and the myosin, so formed, contracts to a slight extent, 

 squeezing out muscle serum. Kiihne found this latter fluid to contain 



(1) A proteid coagulating at 45 C. ; (2) an alkali albumin ; 5 (3) a 

 small quantity of albumin ; (4) extractives and salts. 



A good many years later, I was successful in repeating these ex- 

 periments with mammalian muscle, 6 and showed, moreover, that not only 



1 Salkowski, Centralbl. f. d. med. Wissensch., Berlin, 1894. 



2 Arch.f. d. ges. Physiol., Bonn, 1895, Bd. Ixi. S. 341 ; 1896, Bd. Ixv. S. 90; Schulze, 

 ibid., S. 299 ; 1897, Bu. Ixxii. S. 145. 



3 Munk's "Physiologic," Ann. 4, S. 280. 



4 " Lehrbuch d. physiol. Chem.," S. 272 ; "Untersuch. it. das Protoplasma," Leipzig, 

 1864. 



5 The natural alkali albumins described by older workers are no doubt all globulins. 



6 Halliburton, Journ. Physiol., Cambridge and London, vol. viii. pp. 133-202. 



