GENERAL PROPERTIES AND REACTIONS OF PROTEIDS. 41 



simple method of separating the two classes of proteids. 1 If boiling is omitted, 

 the proteoses are in part precipitated also (C. J. Martin). 



5. The alcohol method. -The solution is rendered faintly acid with acetic acid, 

 and several times its volume of absolute alcohol are added. After twenty-four 

 hours it is boiled and filtered ; the filtrate is proteid-free. 2 The action of alcohol 

 on proteids is peculiar ; it precipitates proteids in the cold ; and the precipitate, 

 if washed free from alcohol, is found to be readily soluble in suitable reagents 

 such as saline solution. But if the precipitate is left in contact with the alcohol 

 for days or weeks, the solubility of the precipitate is lost ; the precipitate has 

 been converted into a coagulum. This loss of solubility, however, does not 

 occur with proteoses and peptone, and thus this is another very good though 

 tedious method of separating native proteids from products of proteolysis. 3 



6. Salicylsulphonic-acid method. This is recommended by Me William. 4 

 The reagent precipitates albumins and globulins ; on heating, the precipitate is 

 coagulated. The same reagent precipitates proteoses ; on heating, the precipitate 

 dissolves, and re-appears on cooling. The reagent does not precipitate 

 peptones. 



7. By boiiinij. In some cases the proteids are precipitated or more properly 

 coagulated by boiling after faintly acidulating the solution. This is the case 

 with the albumins and globulins, and with the proteids which are usually 

 found in morbid urines. For the separation of native proteids from proteoses 

 and peptones, the method is not to be recommended, because boiling with even 

 dilute acids leads to the formation of small quantities of these products of 

 proteolysis. The use of this method has thus produced many mistakes ; it led 

 Struve, Schmidt-Miilheim, and others, to the conclusion that a peptone-like 

 substance exists in milk and in blood ; and more recently Chabrie, 5 by the use of 

 the same method, has described a new proteose-like constituent of blood 

 serum, to which he has given the name "albumone." Chabrie's mistake has 

 been amply demonstrated by R. Brunner. 6 It should be added that Devoto's 

 method is not wholly free from the same objection. 7 



For quantitative purposes the precipitate produced by these several 

 methods may be collected, washed, dried, and weighed, then incinerated, 

 and the ash deducted. Other methods that have been devised are 

 densimetric methods, in which, after removal of the proteid, the loss of 

 specific gravity is multiplied by a constant factor, 8 and methods in which, 

 by Kjeldahl's process, a nitrogen estimation is made in the precipitate 

 produced by some precipitant. Sebelien 9 recommends tannin for this 

 purpose. 



Precipitation l>y neutral salts (German, Aussalzung). There are a 

 number of organic substances which can be precipitated from their 



1 Obermayer, Med. Jahrb., Wien, 1888, S. 375381 ; Starling, Journ. PhysioL, 

 Cambridge and London, vol. xiv. p. 131 ; C. J. Martin, ibid., vol. xv. p. 375 ; Halliburton 

 and Brodie, ibid., vol. xvii. p. 169 ; Halliburton and Colls, Journ. Path, and Bacterial., 

 Edin. and London, 1895, vol. iii. p. 295. 



2 Hoppe-Seyler, "Handbuch," S. 312 ; Schmidt, Arch. f. d. ges. PhysioL, Bonn, Bd. 

 xi. S. 10 ; Hoffman, Virchows Archiv, 1879, November, S. 255. 



3 S. Martin, Goulstonian Lectures, Brit. Med. Journ., London, 1892, vol. i. ; Gourlay, 

 Journ. PhysioL, Cambridge and London, 1894, vol. xvi. p. 32. 



4 Brit. Med. Journ., London, 1891, vol. i. p. 837 ; 1892, i. p. 115. The reaction was 

 previously described by Roch, Pharm. Centr.-BL, Leipzig, 1889, S. 549. 



5 Coii^t. rend. Acad. d. sc., Paris, tome cxiii. p. 557. 



6 Inaug. Diss., Bern, 1894. 



7 M. Matthes, Berl. klin. Wchnschr., Bd. xxxi. S. 351 ; Halliburton and Colls, 

 loc. cit. 



8 Bornhardt, Ztschr. f. anal. C/iem. , Wiesbaden, 1870, S. 149 ; 1877, S. 124 : Huppert 

 and Zahor, Ztschr. f. physiol. Chcm., Strassburg, Bd. xii. S. 467, 484. 



9 Ibid., Bd. xiii. S. 135 ; Konig and Kisch, Ztschr. /. anal. Chem., Wiesbaden, Bd. 

 xxvii. S. 191. 



