110 COLLOIDS IN BIOLOGY AND MEDICINE 



substance is taken up by a solid one with which it is shaken, the 

 accurate determination of adsorption constants would be of the 

 greatest value. They would then be natural constants of the same 

 class as the boiling points, melting points, etc., which definitely deter- 

 mine the nature of the substances under examination. Unfortunately 

 this is not the case. Chemical phenomena and unexplained factors 

 complicate the pure adsorption phenomena, so that at present, in 

 biological questions, it is only of value to determine whether ad- 

 sorption is the predominating force. Investigations in this field 

 are of great importance. Before the advent of physical chemistry 

 and even now, in biological chemistry, it was usual to search for 

 " pure " substances, and to illustrate a phenomenon by a chemical 

 equation. Adsorption experiments have frequently made it clear 

 to us that in a given case such chemical equations do not and 

 could not exist. The studies of H. WISLICENUS on lignin (see p. 

 248), and on the dyeing process by W. BILTZ and H. FREUNDLICH, 

 are selected from among many other classical examples. 



Adsorption experiments for determining distribution are performed 

 by shaking equal quantities by weight, of the most indifferent solid 

 substance obtainable or a gel (charcoal, cellulose) with various dilu- 

 tions of the dissolved substance. The amount of the substance ad- 

 sorbed is usually ascertained from the solution. It is first determined 

 how much active substance is contained in a unit volume of the 

 solution, which is then examined to see how much has been removed 

 by the adsorbent; the difference gives the quantity adsorbed. Thus 

 H. WISLICENUS determined the total solids in the cambial sap of the 

 beech, before and after shaking it with cellulose, and found by taking 

 the difference in weight the amount of colloid that was adsorbed. 



In individual instances the quantity adsorbed was determined 

 from the adsorbent. B. W. Roux and YERSIN treated diphtheria 

 toxin with freshly precipitated calcium phosphate ; they then washed 

 the calcium phosphate well and injected it into guinea pigs. A de- 

 termination by means of the adsorbent instead of the fluid I con- 

 sider erroneous in principle, because it has been shown repeatedly, 

 in well-controlled experiments, that the adsorbed substance under- 

 goes changes at the surface of the adsorbent. 



The fact that a portion of the dissolved substance is removed from 

 the fluid by a solid substance with a large surface does not prove 

 that adsorption has taken place. If, for example, 1 gm. cellulose 

 always removes from a solution the absolutely identical quantity of 

 the dissolved substance, irrespective of the concentration of the 

 solution, we would in all probability be dealing with a chemical phe- 

 nomenon. If the proportion between the adsorbed substance and 



