OF VITAL PHENOMENA 73 



of a suspension or suspensoid sol, although they are probably 

 always killed in the process. The process of agglutination of 

 bacteria consists of two stages: first, the transformation of the 

 bacteria into suspensoid particles by treatment with specific 

 agglutinins or by boiling ; second, the precipitation of these par- 

 ticles by electrolytes. The precipitation of a suspensoid sol is 

 always inaugurated by clumping of the particles. 



Cholesterin and uric acid may form suspensoid sols and gels. 

 Cholesterin appears to form a true solution in the bile, however, 

 and it cannot be detected within the red blood corpuscles by 

 means of the ultramicroscope. 



Lecithin when rubbed up with water forms a sol which is 

 intermediate between a suspensoid and an emulsoid. It re- 

 sembles an emulsoid in that the particles contain water. It re- 

 sembles a suspensoid in that the particles may be easily seen with 

 the ultramicroscope. Within the red blood corpuscles, how- 

 ever, the lecithin cannot be seen with the ultramicroscope and 

 evidently forms part of the emulsoid gel, either due to the differ- 

 ence in the medium or to the fact that it is chemically combined 

 with one or more of the other substances present. 



Emulsoids 



The emulsoids are called hydrophile colloids by Perrin because 

 of their great affinity for water. They are the true colloids, 

 or glue-like substances, according to Graham's definition, except 

 for the fact that some of them may be crystallized with more 

 or less difficulty. When a dry mass of colloid substance is placed 

 in water it absorbs water and swells, with the evolution of heat, 

 forming a gelatinous mass. It usually requires mechanical or 

 other assistance, however, to get it into solution. The colloid 

 particles in sols contain water and the water between them con- 

 tains some dissolved colloid. It is probably for this reason that 

 the particles do not appear distinct with the ultramicroscope. 

 An absolutely pure solution of gelatine appears clear with the 

 ultramicroscope except at certain concentrations and tempera- 

 tures, and if some particles are seen in it they probably are im- 

 purities. Under certain conditions, however, the particles lose 

 some of their water and approach in character the suspensoids, 

 becoming optically more distinct. Similarly, in an absolutely 



