GENERAL PROPERTIES AND RE A CTIONS OF PROTEIDS. 43 



The temperature of heat coagulation of some of the principal proteids 

 may be approximately stated as follows : 



ALBUMINS. 



Egg albumin . . . 73 C. 



Serum albumin (a) . . 73 c 



(0) . . 



. (y) 



Muscle albumin . . 73 C 



Lact-albumin . 77 C 



84 



GLOBULINS. 



Cell globulin . . 48-50 C. 



Fibrinogen . . . 56 ,, 



Serum globulin . . 75 



Myosinogen . . . 56 



Vitellin . . . . 75 



Crystallin ... 73 



Hsemocyanin . . . 68 



With regard to the separation of proteids by the use of the method 

 of fractional heat-coagulation, the opinion has been expressed by Hay craft 

 that the results obtained are not trustworthy. It is probable, nevertheless, 

 that the method is trustworthy, since the proteids so separated can be shown 

 to possess other differences. 1 



Mechanical precipitation of proteids. By mechanical means, such as 

 shaking with sand, or even pouring from one test tube to another, a solution 

 of egg-white deposits threads of insoluble proteid, reminding one of fibrin 

 filaments, which also they resemble in their difficulty of solubility. By 

 prolonged shaking, 96 per cent, of the proteid present may be 

 deposited. Other proteids behave similarly, but as a rule less markedly, 

 namely, egg globulin, vitellin, the proteids of blood plasma, myosinogen, 

 potato proteid, plant vitellin, alkali albumin, and some specimens of 

 caseinogen (Eamsden). 2 



Indiffusibility. The proteids belong to the class of substances called 

 colloids by Thomas Graham; that is, they pass with difficulty or not 

 at all through animal membranes, or vegetable parchment, the substance 

 usually employed in the construction of dialysers. Proteids may thus be 

 separated from diffusible (crystalloid) substances, like sugar and salts. 

 If a mixture of albumin and globulin, dissolved in a saline medium as 

 in blood serum, is placed in a dialyser, with distilled water outside, the 

 salts and extractives pass through the membrane into the water, and 

 water passes in ; the proteids remain within ; the albumin in solution, but 

 the globulin, which is insoluble in water containing no salts, precipitated. 



The term colloid does not necessarily imply that the indiffusible 

 substances are not capable of crystallisation; for many of the pro- 

 teids have now been crystallised; this is particularly the case with 

 the vegetable proteids (p. 52), with haemoglobin (p. 61), with egg 

 albumin, and with serum albumin. F. Hofmeister 3 was the first to 

 crystallise egg albumin ; a solution of egg white is mixed with an equal 

 volume of saturated solution of ammonium sulphate, and the globulin so 



1 The following are the principal papers on this question : Halliburton on "Proteids 

 of Serum," Journ. Physiol., Cambridge and London, vol. v. p. 159; xi. 456; Corin and 

 Berard, "Egg White," Bull. Acad. roy. dc nUd. de Belg., Brnxelles, 1888, tome xv. p. 4 ; 

 Colin and Ansiaux, ibid., 1891, tome xxi. p. 3 ; Haycraft and Duggan, Brit. Mcd. Journ., 

 London, 1890, vol. i. p. 167 ; Proc. Roy. Soc. Edin., 1889, p. 351 ; Centralbl.f. Physiol., 

 Leipzig, Bd. iv. S. 1 ; Fredericq, ibid., Bd. iii. S. 601 ; Chittenden and Osborne on "Corn- 

 Proteids," Am. Chem. Journ., Baltimore, vol. xiii. pp. 7 and 8 ; xiv. p. 1 ; Hewlett, 

 Journ. Physiol. , Cambridge and London, 1892, vol. xiii. p. 512 ; Ramsden, Proc. Physiol. 

 Soc., London, 1892, p. 23; A. di Frassineto, Sperimentale, Firenze, 1895, tome xlix. All 

 the above except Haycraft and Ramsden defend the method. 



2 Arch. f. Physiol., Leipzig, 1894, S. 517. 



3 Ztschr. f. physiol. Chem., Strassburg, Bd. xiv. S. 165; 1892, xvi. S. 187; see also 

 Gabriel, ibid., 1891, Bd. xv. S. 456. 



