166 



COLLOIDS IN BIOLOGY AND MEDICINE 



The Colloid Cleavage Products of Proteins. 



Proteins undergo hydrolytic cleavage by acids, alkalis and 

 enzymes. From the viscosity curve resulting from the prolonged 

 action of NaOH on albumin, it is deduced that the disintegration 

 of albumin depends upon the albumin ions (W. M. BAYLISS, K. 

 SCHORR). T. B. ROBERTSON arrived at a similar conclusion from his 

 studies of the tryptic digestion of casein. Under these circum- 

 stances, it is obvious that, in general, the digestion of albumin by 

 enzymes occurs more readily in acid or alkaline solution than in 

 neutral solution where there are but few albumin ions. 



With increasing subdivision of the molecule, the diffusibility, etc., 

 increases, and the precipitability by neutral salts decreases. The 

 group of cleavage products, known as albumoses, dialyze slowly 

 through animal membranes, whereas the peptones are not to be dis- 

 tinguished in this respect from true crystalloids. That they are 

 still to a certain extent colloids is proved by their forming films on 

 the surface of water (described on p. 33) which places them in the 

 class of those dyes which lie midway between colloids and crystal- 

 loids. H. BECHHOLD arrived at a similar result by separating albu- 

 moses from the remaining fluid by means of uUrafiUration, whereas 

 peptones and the closely related deuteroalbumoses C were not held 

 back even by 10 per cent filters. 



The albumoses and perhaps also the peptones are evidently mix- 

 tures of numerous different substances which have not yet been 

 chemically identified. They are differentiated and classified ac- 

 cording to their precipitability by electrolytes and alcohol, which 

 doubtless stands in a certain relationship to the size of their molecules 

 and particles and to their ionization, see page 152. By means of ultra- 

 filters of different permeability, H. BECHHOLD separated albumoses 

 into various groups which corresponded to their precipitability. 



Subjoined is the classification of F. HOFMEISTER-PICK of the results 

 by ultrafiltration : 



