44 PROTEIDS. 



acids, alkalis, and neutral salts (sodium chloride). These solu- 

 tions give the following characteristic reactions : 



/ 1. Acidulate fairly strongly with acetic acid and add a few 

 drops of saturated solution of sodium chloride ; a precipitate is 

 formed which disappears on warming and comes down again on 

 cooling. If excess of the salt is added the precipitate does not 

 dissolve on warming. 



f 2. Add carefully a few drops of pure nitric acid ; a precipitate 

 is formed if the acid is not in excess, which disappears on warm- 

 ing and comes again on cooling. 



/ 3. Add acetic acid, avoiding all excess, and then a trace of 

 potassium ferrocyanide ; a precipitate is formed which disappears 

 on warming and reappears on cooling. 



/ 4. On the addition of caustic soda in excess and a trace of 

 sulphate of copper the ordinary biuret reaction is obtained, TJijg 

 reaction distinguishes hemialbumose from other soluble proteids. 

 with the exception of peptones. 



Hemialbumose has so far been spoken of as being one uniform 

 substance only. Kiihne and Chittenden in their earlier work 1 at 

 first distinguished merely between a soluble and insoluble form ; 

 more recently they have described four closely allied, but distinct 

 forms of the albumose. 2 (1) Protalbumose. Soluble in hot and 

 cold water and precipitable by NaCl in excess. (2) Deuteroal- 

 bumose. Soluble in water, not precipitated by NaCl in excess, 

 unless an acid be added at the same time. (3) Hcteroalbumose. 

 Insoluble in hot or cold water ; soluble in dilute or more concen- 

 trated solutions of sodium chloride, and precipitable from these 

 by excess of the salt. (4) Dysalbumose. Same as heteroalbumose, 

 except that it is insoluble in salt solutions. 3 Hemialbumose as 

 ordinarily prepared may hence be regarded as a mixture of these 

 several albumoses in varying proportions according to the condi- 

 tions of its preparation. 



The preceding statements as to the existence of four forms of 

 hemialbumose are however contested by Herth, Straub, and Ham- 

 burger (loc. cit. on p. 42). 



The peptones. Kecent work has shewn that in all probabil- 

 ity the various substances which have been described as peptones 

 have consisted to some extent, if not largely, of a mixture of true 

 peptones with variable quantities of albumoses. Our knowledge 

 of the nature and properties of tme peptones is at present in a 



1 Zt. f. Bid. Bd. xix. (1883), T. 174. 



2 Ibid. Bd xx (1884), S. 11. 



3 For further details the original papers of Kiihne and Chittenden must be con- 

 sulted, more especially Zt. f. Biol. Bd. xx. (1884), S. 11. See also Neumeister, Zt f. 

 Bid. Bde. xxm. ( 1887), S. 381 ; xxiv. (1888), S. 267; xxvi. S 324. The preparation 

 and separation of the albnmoses is conveniently given in Kohmann's " Anleitung /urn 

 chemischen Arbeiteu." Berlin, 1890, S. 48. 



