7 6 CHEMICAL CONSTITUENTS OF BODY AND FOOD. 
peptone-like materials on digestion, which differ from true peptones and 
proteoses by not giving the colour reactions in question. 
Fibroin is the substance of which spiders' webs are composed. It 
is insoluble except in concentrated mineral acids and alkalis. It yields on 
decomposition glycocine, leucine, and tyrosine, and gives the proteid colour 
reactions. This substance and sericin, a similar material (which, however, 
gives no glj'eocine on decomposition), are found together in silk. 1 Hammarsten - 
gives the following table of percentage compositions : — 
C 
H 
N 
s 
O 
Conchiolin . 
50-92 
6-88 
17-86 
0-31 
24-34 
Krukenberg. 
Spongin 
46-5 
6 3 
16-2 
0-5 
27-5 
Crookewitt. 4 
j> 
. 48-75 
6-35 
16-4 
Possell. 5 
Cornein 
, 48-96 
5-9 
16-81 
28'33 
Krukenberg. 
Fibroin 
. 48-23 
6-27 
18-31 
27-19 
Cramer. 
j) 
. 48-3 
6-5 
19-20 
26-0 
Yignon." 
Sericin 
. 44-32 
6-18 
18-30 
30-2 
Cramer. 
Inorganic Compounds. 
Water forms about 58"5 per cent, of the weight of the body; 
in infants it is 6Q-4: per cent. An adult takes in food 2,500 c.c. of 
water daily, and excretes rather more, as some is formed in the body 
by the oxidation of hydrogen. 
Hydrogen peroxide is stated by A\ urster 8 to be given off in various 
situations ; he uses tetramethvl-paraphenylenediamine papers to detect 
it. 
Hydrogen sulphide occurs in small quantities as the result of putre- 
factive changes in the alimentary canal. 
Ammonia is also formed in putrefactive processes, and in pancreatic 
digestion. A small quantity occurs in fresh urine, and increases when 
the urine putrefies. 
Hydrochloric acid occurs in gastric juice. 
Carbonic acid occurs in the blood, lymph, and secretions. 
The acids found in the body are, however, usually in combination as 
salts. 
Salts. — The chief salts found are the chlorides of sodium and potassium, 
the sulphates of the same metals, phosphates of sodium, potassium, 
calcium, and magnesium, carbonates of sodium and calcium. Bone, 
dentine, and enamel are chiefly rich in calcium salts, especially the 
phosphate. Other solid tissues are especially rich in potassium salts. 
In the fluids (milk excepted) the most abundant salt is sodium chloride. 
A fuller consideration of the various saline constituents will be taken with 
the individual tissues and secretions. The following general tables may be, 
however, quoted here ; p the figures give percentage quantities of mineral 
matters in the ash : — 
1 Weyl, Ber. d. deiUsch. chem. Gesellsch., Berlin, Bd. xxi. S. 1407, 1529. 
- " Physiol. Chem.," 3rd German edition, S. 49. 
3 Ber. d. deutsch. chem. Gesellsch., Berlin, Bd. xvii. 
4 Ann. d. Chem., Leipzig, Bd. xlviii. s Ibid., Bd. xlv. 
s Journ. f. prakt. Chem., Leipzig, Bd. xevi. 
7 Corrupt, rend. Acad. d. sc., Paris, tome exv. 
8 Ber. d. deutsch. chem. Gesellsch., Berlin, Bd. xiw S. 3195 ; xx. S. 263, 1033. 
9 From Beaunis, " Physiologie humaiue." 
