560 INFECTION AND RESISTANCE 



systems must be in the main colloidal. All biochemistry is thus in 

 the main colloid chemistry. Aside from mineral salts, urea, uric 

 acid, and a few other bodies, the reagents and products which are 

 active in life processes are all to be found in the living organism 

 in the colloidal state. While crystalline directive forces are in gen- 

 eral absent, we have nevertheless to deal in biological phenomena 

 with a great variety of directive forces of a wholly different charac- 

 ter. Colloidal substances in high degrees of dispersion such as 

 proteins and the like in the alimentary fluids are being continually 

 converted into active living tissues, a process manifestly involving 

 very definite directive forces, since the product (the tissue cells) 

 is an organized one, even though its organization is not similar to 

 that of a crystal. Thus the building of living tissue involves 

 among other things the conversion of sols of many sorts (alimen- 

 tary fluids, blood, etc.) into gels. In other words, the living 

 tissue is to a certain extent to be looked upon as a colloidal gel, dif- 

 fering, however, from laboratory gels in possessing a definitely or- 

 ganized cell structure. While it is true that in the spontaneous gel 

 formation with certain colloids, as, for example, gelatin, myelin, or 

 web structures are formed purely as a result of the physical and 

 chemical forces active, these cannot be said to bear any very strong 

 resemblance to living cells. It is thus apparent that life processes 

 differ very materially from those of the chemical laboratory. On the 

 other hand, it is true that many of the component reactions which go 

 to make up the life process may be very closely duplicated by labora- 

 tory means, and that already the study from the colloid chemistry 

 point of view of the reaction of many of the substances which go to 

 make up the living organism has given interesting and important 

 results. Furthermore, the whole field of colloid investigation has 

 been greatly stimulated by the hearty support and encouragement 

 which it has received from biologists. Some slight attempt will be 

 made here to illustrate by a few examples the far-reaching possi- 

 bility of explanation which colloid chemistry offers of certain phases 

 of biological science. The actual accomplishment in the field is 

 already so great that only a very limited discussion can be offered 

 here. 



2. The action of electrolytes on emulsions of bacteria is wholly 

 analogous to their action on colloidal suspensions. The bacterial 

 emulsions are very sensitive to flocculation by mineral acids, one thou- 

 sandth normal hydrochloric and sulphuric acids usually being suffi- 

 cient to cause complete clumping and settling of the bacteria. Xeu- 

 tral salts, with the exception of those of silver, mercury, iron, and 

 aluminium, do not flocculate the bacteria. If, however, the bacteria 

 are first treated in the absence of electrolytes with an agglutinating 

 serum small concentrations of salt solutions will bring about floccu- 

 lation. It is also known that bacteria have the power of absorbing 



