CHAP. I.] THE PROTEIDS. 19 



these processes be imitated in the laboratory ? Only in part, indeed, for, 

 in spite of certain statements to the contrary, no one has given valid 

 proof of having, by an artificial oxidation, obtained urea. 



The following are the chief facts which have been discovered in 

 reference to the decomposition of proteids ; after quoting these we shall 

 refer to some of the theoretical views to which they have given rise. 



1. Action of water. When heated with water in sealed tubes at a 

 temperature of 100 C., the proteids are in part dissolved, the solution 

 afterwards undergoes decomposition, it being found to contain sulphur- 

 etted hydrogen, and a number of complex bodies of which some are 

 soluble in alcohol and ether (Gautier). 



2. Action of heat. When subjected to dry distillation, the proteids 

 furnish the oily liquid long known as Dippel's oil, which contains 

 (1) ammoniacal salts of the fatty acids, as ammonium butyrate, valerate 

 and caproate; (2) amines, derived from the monatomic alcohols, viz. 

 methylamine, propylamin^ butylamine ; (3) aromatic compounds, as ben- 

 zine, aniline, phenol ; (4) picoline and lutidine, which are bases which 

 combine with the iodides of alcohol radicals to form compound ammonium 

 iodides. 



3. Action of putrefaction. When exposed to the combined influences 

 of air and moisture, especially at a high temperature, the proteids yield 

 ammonia, ammonium sulphide, carbon dioxide, volatile fatty acids, lactic 

 acid, amines, leucine and tyrosine. Uncjer certain circumstances indol may 

 be formed. 



4. Action of strong mineral acids and of caustic alkalies. Prolonged 

 boiling with sulphuric and hydrochloric acid and fusion with caustic 

 alkalies gives rise to products of which the chief are the same in the two 

 cases, viz. leucine, tyrosine, aspartic acid and glutamic acid. 



When proteid bodies are treated with dilute acids they undergo hydro- 

 lytic decomposition, and certain definite compounds may be extracted from 

 the resulting mass. Their proportion is however small in comparison with 

 the by-products which we have no means of investigating. 



The term "liydrolytic decompositions" has been applied by Hermann 1 to designate 

 decompositions in which a body splits up after combining with the elements of water; 

 thus under various circumstances the neutral fats combine with the elements of water 

 and decompose into a fatty acid and glycerin, as shewn in the case of stearin by the 

 following equation: 



^HiioO^ + 3H 2 O = JJC 18 H^ + CsH^V 



Stearin. Water. Stearic acid. Glycerin. 



Nasse first observed that the nitrogen in proteids appears to exist in two 

 conditions, as evidenced by the fact that a certain fraction of it is much 

 more unstable, apparently more feebly combined, than the rest. Schutzen- 

 berger has fully confirmed these observations. He heated proteids with 

 caustic baryta, in aqueous solution, up to 100 and collected the ammonia 

 given off in sulphuric acid. There separated a good deal of granular 

 matter, which increased as the reaction proceeded and which was found to 

 consist of carbonate, a little sulphate, oxalate, and phosphate, of barium. 



1 Hermann, Elements of Human Physiology, 2nd English ed., p. 2. Smith, Elder 

 and Co., 1878. 



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