226 CHEMISTRY OF THE PROTEIDS CHAP. 



Weber, 1 Heine, 2 Walker and Appleyard, 3 Albert Mathews, 4 Vignon, 5 

 Prud'homme, 6 Wichmann, 7 Gillet, 8 Nietzki, 9 Hallit, 10 Macallum, 11 

 Martin Heidenhain, 12 Bethe, and others. 



Albert Mathews in 1898 pointed out that albumins and albumoses, 

 being weak bases, readily unite with free acids to form salts which may 

 be either soluble or insoluble. Thus, on adding to albumin or albumose 

 a solution of the free picric acid, metaphosphoric, molybdic, tungstic, 

 phosphotungstic, tauric, stearic, or chromic acids, a coagulum is formed 

 at once. Should these acids be employed in the form of their salts, 

 no precipitate is formed till by the addition of a few drops of acetic 

 or hydrochloric acid the solution containing, for example, the mixture 

 of albumose and sodium picrate has been rendered slightly acid. 

 Whenever the acid is added the albumose picrate is thrown down at 

 once, " probably because the acetic acid sets free the picric acid." All 

 the colour acids used by histologists react in exactly the same manner. 

 These dyes are employed generally in the form of neutral salts, and 

 require the addition of some acidifier, when they at once combine with 

 the albumin, forming a dense coagulum Mathews obtained in this 

 way albumin and albumose precipitates with acid-fuchsin, acid-green, 

 nigrosin, aniline-blue-black, erythrosin, Congo-red, methyl-blue, sodium 

 carminate, and indigo -carmine by using acid (or alkaline, see later) 

 solutions of albumins and albumoses. " This reaction of the acid stains 

 indicates beyond doubt that these stains, when in acidulated solutions, 

 will enter into chemical combination with the albumose- or albumin-mole- 

 cule like any other acid. Inasmuch as it is possible that the free 

 acids enter one or more of the basic NH 2 -groups of the albumin-mole- 

 cule, the acid stains also probably enter this group." Colour-bases car 

 also be made to unite with albumin and albumoses : if lead acetate is 

 brought into a neutral solution of albumin or albumose nothing happens, 



1 Weber, Journ. of Soc. Ghem. Industr. 13. 120 (1894). 



2 Heine, Zeitschr. f. physiol. Ghem. 21. (1895). 



3 Walker and Appleyard, Trans. Ghem. Soc. (1896), p. 1334. 



4 Matthews, Amer. Journ. of Physiai. 445-454, July 1898. 



5 Vignon, Oompt. Rend. 357-360 (1897) ; abstract in /. Soc. Ghem,. Indus. 1 014 

 (1897). 6 Prud'homme, Rev. G$n. des. Mat. Col. 2. 213 and 4. 72. 



7 A. Wichmann, Zeitschr. f. physiol. Ghem. 27. 575 (1899). 



8 C. Gillet, Rev. G'en. des Mat. Col. 4. 183-9 (1900). 



9 Nietzki, Chemie d. organisch. Farbsto/e, 1901. 



10 Hallit, Journ. Soc. Dyers and Colourists, 15. 30 (1899) ; abstract in J. Soc. Ghem, 

 Indust. (1899), pp. 368-70. 



11 Macallum, Journ. of Physiol. 22. 92-98 (1897). A complete abstract is given ii 

 Mann's Physiological Histology (1902), pp. 290, 291, 294. 



12 M. Heidenhain, Pfliiger's Arch. /. d. ges. Physiol. 90. 115 bis, 230 (1902), 90, 

 440 (1903) ; Munchener Medizin. Wochenschr. 1902, No. 11 ; Zeitschr. f. iirissenschaftl 

 Mikroskop. u. mikrosk. Technik, 19. 431 (1902). 



