290 [Dec. 1, 



quired for building up the tissues of the living organism. Although 

 the two classes are widely separated in their properties, a complete 

 parallelism appears to hold between them. Their existence in nature 

 seems to call for a corresponding division of Chemistry into a Cry- 

 stalloid and a Colloid department. In many cases the same body 

 may be obtained either in the crystalloid or in the colloid modifica- 

 tion. The chemistry of the two classes is distinct, and the reactions 

 of the same body are different according as it is in the crystalloid or 

 the colloid form. Chemists have been enabled to apprehend properly 

 a number of anomalous facts and discrepancies in the reactions of 

 various substances which were supposed to be identical until Mr. 

 Graham had called attention to this important molecular difference 

 in their structure. He has shown that the crystalloid is the static, 

 as the colloid is the dynamic condition of a body : the usual tendency 

 of the colloid is a gradual approach towards the crystalloid form. 



The method by which Mr. Graham has obtained these important 

 results is characterized by that simplicity which so eminently di- 

 stinguishes the mode in which he has proceeded during the whole of 

 this lengthened and important inquiry. The memoir contains a 

 description of the process, which he names Dialysis, for separating 

 a crystalloid from a colloid ; and it is scarcely necessary to insist 

 upon the practical importance which this method possesses. In the 

 examination of organic mixtures for poisons which, like the vegetable 

 bases, are crystallizable, it will afford most valuable aid, as it separates 

 the poison without adding anything except a little pure water. Many 

 organic colloids, such as gum, albumen, or caramel, may by its means 

 be readily freed from saline impurities, which can scarcely be removed 

 by any other known means. Its application to the recondite pro- 

 cesses of secretion, and to many of the chemical changes taking place 

 in the living organism, need not be insisted on. The door thus 

 opened to further inquiry will no doubt be eagerly entered by the 

 physiological chemist, who can hardly fail of obtaining new insight 

 into the obscure but deeply important operations of the nutrition, 

 reparation, and removal of tissue. 



MR. GRAHAM, 



In receiving this Medal, the highest honour which it is in the 

 power of the Royal Society to award, you will accept it as a testi- 



