GENERAL PROPER PIES AND PP.. I CTIt >NS OF PR0TE1DS. 43 
The temperature of heat coagulation of Borne of the principal proteids 
may be approximately stated as follows: — 
A.LBDMIKS. 
1 rLOBULINS. 
Egg albumin 
73° C. 
Cell globulin . 
48' 
-50° C 
Serum albumin (a) . 
73° „ 
Fibrinogen 
56°,, 
OS) • 
77° „ 
Serum globulin 
75° „ 
. (r) • • 
&4°„ 
Myosinogen 
56° „ 
Muscle albumin 
73° „ 
Vitellin . 
75° „ 
Lact-albumin . 
77° „ 
( Jrystallin 
Hsemocyanin . 
: 
73' „ 
68° „ 
With regard to the separation of proteids by the use of the method 
of fractional heat-coagulation, the opinion has been expressed by Haycraft 
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, 90 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 
IndiffusiMlity. — 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 Sernm," Journ. Physiol., Cambridge and London, vol. v. p. 159; xi. 456; Corin and 
Berard, "Egg White," Bull. Acad. roy. de m6d. de Belg., Bruxelles, 1888, tome'xv. p. 4 ; 
Colin and Ansiaux, ibid., 1S91, tome xxi. p. 3 ; Haycraft and Duggan, Br if. Med. Journ., 
London, 1890, vol. i. p. 167 : Proc. Boy. Soe. Bdin., 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 ; Bamsden, Proc. Physiol. 
Soc, London, 1892, p. 23; A. di Frassineto, Sperimentale, Firenze ; 1S95, tome xlix. All 
the above except Haycraft and Bamsden defend the method. 
'Arch. f. Physiol., Leipzig, 1894, S. 517. 
8 Ztschr. f. physiol. Chem., Strassburg, Bd. xiv. S. 165; 1892, xvi. S. 187; see also 
Gabriel, ibid., 1891, Bd. xv. S. 456. 
