146 COLLOIDS IN BIOLOGY AND MEDICINE 



exact knowledge of the mechanism of the reaction, seems to me to be 

 a still more advanced step. 



Adsorption by protein in solution is more important than ad- 

 sorption by solid proteins. By ultrafiltration it might be possible to 

 investigate the distribution between a dissolved colloid and a crystal- 

 loid. In this connection I am acquainted only with the investiga- 

 tions of H. BECHHOLD on the distribution of methylene blue between 

 water and serum albumin (see p. 26). 



THOMAS GRAHAM and R. O. HERZOG* G determined the coefficient of 



D cm 2 



diffusion of egg albumin and ovomucoid to be : f- 10 5 . Its 



seconds 



values are in the case of 



Egg albumin 0.063 (at 13 C.) measured by GRAHAM, calculated by 



STEFAN. 



Egg albumin 0.054 (at 15.3 C.) according to HERZOG. 



Egg albumin 0.046 (at 7.75 C.) according to HERZOG. 



Egg albumin [crystallized with 3.6% 0.081 (at 16 C.) according to 



DABROWSKI* (NH 4 ) 2 SO 4 ]. 



Ovomucoid 0.034 (at 7.75 C.) according to HERZOG. 



Glucose 



(for comparison) . 0.57 (at 18 C.) 



From these figures the radius r of albumin particles has been 

 calculated for 



Salt-free egg albumin 2,43 up. 



Crystallized egg albumin 1,37 w 



[with 3.6% (NH 4 ) 2 SO 4 ] 



This diminution in the size of the albumin particles in the presence of 

 (NH 4 ) 2 SO 4 coincides with what we shall learn of the other effects of 

 neutral salts on albumin (see p. 151). 



When solid albumins go into solution there occurs a diminution 

 in volume amounting to about 5-8 per cent, as is the case with 

 starches. (H. CHICK and C. J. MARTIN.*) 



Egg albumin and serum albumin, globulin, casein and fibrin have 

 been most carefully studied colloid chemically. 



ALBUMINS. 



Albumins are soluble in water, and in dilute neutral salt, and in 

 acid and in alkaline solutions. They are usually found in the com- 

 pany of globulins and there are reasons for believing that they may 

 be converted into globulins by moderate heating. Albumins occur 

 almost exclusively in serum, in eggs and in milk; the existence of 

 plant albumins is not yet definitely established. 



