SYMPOSIUM ON COLLOIDS 47 



Of the three general types of colloids only one, the sol, 

 has been mentioned in the preceding discussion. A sol may be 

 defined as a solid dispersed in a liquid medium. Discussion of 

 the emulsoids, or liquids dispersed in liquid media, and of 

 gels, or liquids dispersed in solid or semi-solid media, must be 

 omitted both because of their complexity and because of lack 

 of time. 



In conclusion, it may be said that the scientific and practical 

 results of the study of colloids have amply repaid for the ardu- 

 ous researches made upon them and we may look for similar 

 if not greater results from the researches to be made in the 

 near future. 



SIGNIFICANCE OF COLLOIDAL CHEMISTRY 



IN PHYSIOLOGY 



By William Crocker, University of Chicago. 



I. INTRODUCTION 



Were we to put today to a large number of physiologists the 

 question, "How much, in your opinion, will the laws of col- 

 loidal chemistry illuminate and explain physiological phe- 

 nomena?" we would get a great diversity of opinion. We 

 would find on one extreme those who believe that the newer 

 branch of chemistry has not led and will not lead to any con- 

 siderable advance in physiology and, on the other, those who 

 see almost all the problems of biology rooted in colloids and 

 almost all the phenomena peculiar to the living organism find- 

 ing explanation in the simple laws of heterogeneous systems. 

 With colloidal chemistry in many of its phases a new science 

 and with many of its fundamental laws even now just being 

 established, it is evident that the application of its principles 

 to the complex phenomena of living organisms is a thing to 

 be done with some caution. 



The application of the laws of homogeneous solutions to 

 biology has already answered many questions and is still to 

 answer many more. It is likewise evident that it will leave 

 perhaps a greater number, unanswered or explained only on 

 the assumption of vital principles. The laws of heterogeneous 

 solutions are now having their turn at vital problems with ex- 

 cellent prospects of solving many of these along physical 

 chemical lines. To date, however, the significance of colloidal 

 chemistry in biology is more a matter of hope and excellent 

 outlook than of actual accomplishment. This prospect can 



