76 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 glycocine on decomposition), are found together in silk. 1 Hammarsten ' 2 

 gives the following table of percentage compositions : 



INORGANIC COMPOUNDS. 



Water forms about 5 8 -5 per cent, of the weight of the body ; 

 in infants it is 664 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 "Wiirster 8 to be given off in various 

 situations ; he uses tetramethyl-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. 



Carlonic 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 ; 9 the figures give percentage quantities of mineral 

 matters in the ash : 



1 Weyl, Ber. d. deutsch. chem. Gesellsch., Berlin, Bd. xxi. S. 1407, 1529. 



2 " Physiol. Chem.." 3rd German edition, S. 49. 



3 Ber. d. deutsch. chem. Gesellsch., Berlin, Bd. xvii. 



4 Ann. d. Chem., Leipzig, Bd. xlviii. 5 Ibid., Bd. xlv. 

 Journ. f. prakt. Chem., Leipzig, Bd. xcvi. 



7 Compl. rend. Acad. d. sc., Paris, tome cxv. 



8 Ber. d. deutsch. chem. Gesellsch., Berlin, Bd. xix. S. 3195 ; xx. S. 263, 1033. 



9 From Beaunis, " Physiologic humaine." 



