AND MEDICINE 



solutio = solution). We speak of silver sols, albumin sols, etc. The 

 dissolved substance in a sol may by various means be separated in an 

 amorphous form that retains more or less water. This form is called 

 a gel 1 (from similarity to gelatin). If we add salt to a solution of 

 colloidal silver, we obtain a black sediment containing very little 

 water, the silver gel. If we boil a serum solution, the entire mass 

 solidifies to a jelly that does not allow a separation of water and 

 albumin, the albumin gel. 



Sols. 



As the researches of GRAHAM have already shown, sols in general 

 are substances which subdivide in their solvents into relatively 

 large particles, or which possess very large molecules, so large that, 

 in contrast with the molecules of water or crystalloids, they are un- 

 able to pass through the pores of an animal skin or a parchment 

 membrane. Chemical grounds indicate that albumin possesses a 

 very large molecule. Even though we were to assume that it split 

 into single molecules in aqueous solution, these are so large that 

 they are unable to pass through an animal or vegetable membrane. 

 Accordingly, the intact membranes of the organism protect it from 

 loss of albumin; only in pathological conditions as in diseases of the 

 kidneys does albumin pass through. 



Substances like albumin, 2 soluble starches, etc., are to a certain 

 extent inherently colloids. Every further subdivision of the colloid- 

 ally dissolved particles would have to be associated with a splitting 

 of the molecule, and the fragments are certainly no longer albumin, 

 but albumoses, polypeptids, amino-acids, etc. 



It is otherwise in the case of certain artificial colloids. Accord- 

 ing to G. BREDIG and TH. SVEDBERG, gold, silver, platinum and 

 other metals may be electrically pulverized under water or in organic 

 fluids (e.g., isobutyl alcohol). According to G. WEGELIN, silica, 

 vanadic acid, and other substances may by mere trituration be 

 reduced to suspensions whose particles are so small that they can- 

 not be recognized microscopically. If the electrical pulverization is 

 accomplished in water which is practically free from electrolytes, we 

 obtain a solution which is red in the case of gold, brown in the case 

 of silver, and greenish black with platinum. These solutions remain 



1 Many recent authors make "gel" and "jelly" synonymous. It seems 

 preferable to me to use the expression "gel" for the general comprehensive 

 phenomenon and to reserve the word "jelly" for the gelatinization of a hydro- 

 phile colloid. 



2 When I refer to albumin, I mean albumin absolutely unsplit, whether it 

 be egg albumin or globulin, etc., as opposed to albumoses which are classified 

 as albumins in some textbooks. 



