134 PEPTONES. [BOOK u. 



PEPTONES. 



Whatever the intermediate products, the ultimate products which 

 result from the action of gastric juice, natural or artificial, are bodies 

 which, as stated previously, were first designated peptones by Leh- 

 mann. We have pointed out that Meissner distinguished several 

 peptones, which differed in certain reactions one from another. Until 

 lately, the characteristic reaction upon which general reliance was 

 placed, in determining whether a body was a true peptone or not, 

 was the so-called 'biuret' reaction, i.e. the production of a rose-red 

 colour with a minute quantity of solution of copper sulphate, followed 

 by a very large excess of sodium or potassium hydrate. 



The researches of Kiihne have, however, revealed the fact that 

 the biuret reaction is not distinctive of the true peptones, being 

 shared by the albumoses, though the several bodies belonging to this 

 class do not exhibit the reaction in an equally distinct manner, the 

 slightest excess of copper leading in the case of hetero-albumose to 

 the production of the- violet colour which all the native albumins and 

 their compounds exhibit, and which masks the rose colouration at 

 first shewn. Other facts, observed chiefly by Kiihne and Chittenden, 

 have demonstrated that Meissner's a and @ peptones consisted of 

 albumoses. 



This being the case, the question arises : how shall we distinguish 

 the bodies to be termed true peptones? Although the distinction 

 which, following the example of Kiihne and other recent writers and 

 investigators on this subject, we shall draw may be considered by 

 some arbitrary, yet it appears convenient and correct. 



It has been found 1 that ammonium sulphate added, to complete 

 saturation, to solutions of albuminous substances which have been 

 first of all neutralised and then rendered very faintly acid by a 

 trace of acetic acid, precipitates all proteids including the several 

 albumoses, with the exception merely of the bodies which we shall 

 designate as peptones, which are left in solution. 



Some 2 appear to think a distinction, based upon the action of a 

 single reagent, artificial and unphilosophical, and, indeed, were this 

 the case, it would be impossible to defend it. But as a matter of 

 fact, the distinction does not rest upon the action of a single reagent. 



1 J. Wenz, ' Ueber das Verhalten der Eiweissstoffe bei der Darmverdauung.' 

 Zeitschr. f. Biologic, Vol. xxn. (1886), see p. 10. Heynsius had recommended am- 

 monium sulphate as a general precipitant, not only for the native albumins and 

 their derivatives, but for propeptone and peptone. It would appear from Wenz's ob- 

 servations, however, that Heynsius can only have experimented with albumoses and 

 not with true peptones, as the latter were found not to be precipitated by the ammo- 

 niacal salts. 



2 Hammarsten, Lehrbuch d. physiologisch. Cliemie. 



