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, 77'4 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 lie 
subjected to artificial digestion before extraction with ether ; flesh then 
yields an additional - 75 per cent, of fat. 
The following table 3 gives the chief substances in some of the principal 
meats used as food : — 
Constituents. 
Ox. 
Calf. 
Pig. 
Horse. 
Fowl. 
Tike. 
Water ..... 
767 
75-6 
72-6 
74-3 
70-8 
79-3 
Solids 
23-3 
24-4 
27-4 
25-7 
29-2 
20 -7 
Proteids and gelatin 
20-0 
19-4 
19-9 
21-6 
227 
18-3 
Fat 
1-5 
2-9 
6-2 
2-5 
4-1 
07 
Carbohydrate .... 
0-6 
0-8 
0-6 
0-6 
1-3 
0-9 
Salts 
1-2 
13 
1-1 
1-0 
1-1 
0-8 
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, Ccntralbl. f. d. med. JVisscnsch., Berlin, 1894. 
2 Arch. f. d. ges. Physiol., Bonn. 1895, Bd. lxi. S. 341 ; 1S96, Bd. lxv. S. 90 ; Sclmlze, 
ibid., S. 299 ; 1897, Bd. lxxii. S. 145. 
3 Munk's "Physiologie," Aufl. 4, S. 280. 
4 "Lehrbuch d. physiol. Chem.," S. 272 ; "Untersncli. ii. das Protoplasma," Leipzig, 
1864. 
5 The natural alkali albumins described by older workers are no doubt all globulins. 
,; Halliburton, Journ. Physiol., Cambridge and London, vol. viii. pp, 133-202. 
