NITROGENOUS PRINCIPLES. 43 



have been regarded, in accordance with a theory of Mulder, 

 as compounds of a principle, proteine, which is supposed to 

 consist of the four elements in the proportion referred to, and- 

 sulphur or phosphorus. Proteine, according to Mulder, 

 contains C 40 N 5 H 31 Oi 2 , and the albumen of egg might be 

 indicated as consisting of proteine lOeq. -f leq. of sulphur 

 and leq. of phosphorus. The objections to the proteine 

 theory are, that no such compound perfectly free from sulphur 

 exists; with regard to the phosphorus, regarded as charac- 

 teristic of some substances, it probably only exists in animal 

 tissues, in the form of salts of phosphoric acid; Mulder's 

 formulae have been proved erroneous. The expression ' pro- 

 teine compound' is, however, still used to indicate the albu- 

 minoid group. 



The nitrogenous substances are characterised by the pre- 

 sence of sulphur in them, by the absence of any crystalline 

 form, by the complex chemical constitution above referred to, 

 and which renders them most unstable compounds ; they yield 

 at once to -chemical changes when separated from the living 

 organism, and especially if exposed freely to air, under the 

 combined influence of heat and moisture. 



The albuminoid substances agree in certain chemical 

 characters : " They dissolve, with the aid of heat, in potash, 

 and the solution blackens the salts of lead, proving that part 

 at least of the sulphur is present in an unoxidised state. 

 They all dissolve, with the aid of heat, in strong, hydrochloric 

 acid, yielding, if air be admitted not otherwise a purple 

 solution, which after a time changes to a dark brown. The 

 very acid liquid which is obtained by dissolving mercury in 

 its own weight of nitric acid, gives a very intense red colour 

 to all these substances. This character is so well marked, 

 that we can in this way detect the presence of 1 part of albu- 

 men in 100-000 of water. When oxidised by sulphuric acid 



