364 PHYSIOLOGICAL CHEMISTRY. 



Teeth are similar in composition to bone, but contain even 

 less of organic matter ; the enamel containing as much as 96 to 

 98 per cent, of inorganic matter; traces of fluorides and silicium 

 are found in the teeth. 



Hair, nails, horns, hoofs, feathers, epithelium, are nearly identical 

 in composition. They all contain a nitrogenous substance, 

 termed keratin, which is probably not a distinct chemical com- 

 pound, but a mixture of several substances similar in composi- 

 tion and properties. 



Mucus is secreted by the various mucous membranes, and is 

 found in saliva, bile, connective tissues, feces, urine, etc. When 

 pure it forms a clear, translucent or viscid mass ; it contains a 

 substance termed mucin, which swells up in water, and readily 

 dissolves in water containing an alkali ; from these solutions it 

 is precipitated by acetic acid. 



Muscles contain fibrin, albumin, myosin, kreatin, C 4 IT 9 l!^ 3 O 2 , 

 sarkin, C 5 II 4 N 4 0, xanthin, C 5 II 4 N 4 2 , uric acid, glucose, inosite, 

 lactates, and salts. 



Kreatin, sarkin, and xanthin are substances formed in the 

 organism by oxidation of proteids, and may be looked upon as 

 compound ureas or substances formed as intermediate products 

 of the final conversion of proteids into urea, carbon dioxide, 

 water, etc. These substances may indeed be decomposed arti- 

 ficially, in such a manner that urea is produced as one of the 

 prodtrcts of decomposition. 



Brain consists of so many individual parts that the analysis of 

 it as a whole is of little value, and to separate these parts suc- 

 cessfully is a task not yet accomplished. Brain, as a whole, 

 contains cerebrin, lecithin, neurin, cholesterin, and many other 

 substances, some of which are distinguished by the large quan- 

 tity of phosphorus they contain. 



QUESTIONS. 



501. What three kinds of matter are found as constituents of the 

 animal body, and how can they be determined quantitatively ? 



502. Mention the chief constituents of blood, and state those which 

 predominate in serum and in the corpuscles respectively. 



