54 ILLINOIS ACADEMY OF SCIENCE 



III SOME GENERAL CHARACTERISTICS OF CELL COLLOIDS 



The protoplasm is optically isotropic, while some of its 

 products (starch grains, cell walls and crystalloids) are optic- 

 ally anisotropic. It is believed that the double refraction of 

 starch grains and cell walls can be explained on the basis either 

 of impregnating materials, as in the cuticle, or tension within 

 the gels of these structures ; and that the property furnishes no 

 argument in favor of their crystalline structure as against 

 their hydrogel nature (1). With time, however, it seems that 

 the line between crystalline and amorphous bodies becomes 

 distance. (12: pp. 66-75). 



The colloidal constituents of the living cell bear negative 

 charges. As a result living cells themselves are electroneg- 

 ative. This has been shown for lecithin, chlesterin, proteins, 

 chlorophyll, blood corpuscles, bacteria and spermatozoa. 



When Graham divided matter into two classes — crystalloids 

 and colloids — he thought these two divisions were quite dis- 

 tinct. One of the principal characteristics for distinguishing 

 the two classes was their diffusibility through gelatin or other 

 colloidal membranes. We know that the two classes of sub- 

 stances are not so distinct but that colloidal solutions range in 

 their degree of dispersion from suspensions with microscopic- 

 ally visible particles, on one extremity to molecular dispersions 

 on the other. The hydrophyllous colloids of the living body, 

 which are of greater interest to the biologist, are very highly 

 dispersed, approaching in general the molecular state. It is 

 now well known, for example, that haemoglobin forms a 

 molecular solution. Along with this very high dispersion they 

 have the character of diffusing with ease through a variety of 

 colloidal membranes. Egg albumin and haemoglobin diffuse 

 through gelatin plates. Pepsin diffuses into cubes of coagu- 

 lated albumin. The immunity bodies diffuse through a great 

 variety of colloidal membranes (gelatin and agar plates, dead 

 intestine walls and others). This raises the question of how 

 they are retained within the living cell. This question becomes 

 especially urgent if Ruhland (13) is correct in his conclusion 

 that for colloidal solutions the protoplasm acts as an ultra filter. 

 We shall later see his explanation for the retention of certain 

 enzymes by the cell and their localization within it. 



IV WATER RELATIONS OF CELL COLLOIDS 



There are certain characters of hydrophyllous gels and sols 

 that are assuming great importance physiologically. One of 

 the more significant is the water absorbing power of these as 

 affected by various reagents. Water absorption by gels and 



