COLLOIDS IN BIOLOGY AND MEDICINE 



CHAPTER I. 

 WHAT ARE COLLOIDS? 



IN spite of the fact that they have a much wider distribution than 

 crystalloids, it is only a little over fifty years that colloids have been 

 scientifically studied. Plants and animals and all the things we manu- 

 facture from them, such as our clothing and the greater part of our 

 household goods, are colloids. In the year 1861, THOMAS GRAHAM,* l 

 an Englishman, called attention to the fact that there were substances 

 which, when in solution, diffused through parchment membranes (dia- 

 lysed). These he called crystalloids because the soluble crystallizable 

 substances (e.g., sugar and salt) possess this property to a marked de- 

 gree. Substances which were held back by parchment membranes 

 he called colloids, "glue-like," because glue was the most character- 

 istic of this group. Every discoverer of a new fundamental principle 

 is easily led into exaggerations; it so happened with GRAHAM who 

 opposed crystalloids to colloids as "two distinct worlds of matter/ ' 

 though we know now that all sorts of transition stages exist. 



In succeeding years very few investigators concerned themselves 

 with colloids. The very fruitful development of organic chemistry 

 occupied the attention of investigators, who neglected, as less 

 important, a field which promised fewer immediate results. Only 

 in the beginning of the new century was there a revival of interest 

 in colloid chemistry. 



We shall not follow the historic development further, but shall 

 give a description of colloids in accordance with the present state of 

 the science. It must be noted at the outset that, even to-day, the 

 behavior of a dissolved substance towards a partitioning membrane, 

 that is, inability to diffuse through it, is the chief characteristic of 

 a dissolved colloid. 



Many colloids form with liquids, especially with water, a more or 

 less fluid solution. [The term dispersion is preferred by ARTHUR W. 

 THOMAS in a recent discussion on Nomenclature. Science, N. S., 

 Vol. XLVII, No. 1201, p. 10. Tr.] This solution is called a sol (from 



1 An * after an author's name refers to the reference in the index of authors. 



3 



