SYMPOSIUM ON COLLOIDS w 



IX TOPICS IN COLLOIDAL CHEMISTRY AND THEIR BEARING UPON 



PHYSIOLOGY 



Almost any topic commonly discussed under hydrophyllous 

 colloids can also be discussed in important biological relations. 

 Let us select three of a considerable number of such topics for 

 brief consideration : hysteresis, protective action of hydro- 

 phyllous colloids, and the anion series of alkali salts. 



Hysteresis, or spontaneous ageing changes, so common in 

 colloids has many points of physiological interest. These are 

 well illustrated in vitro by the slow or rapid fiocculation of any 

 colloidal solution ; by the reaction between immune bodies be- 

 coming irreversible with time and by changes in the vapor 

 tension of gels, continuing for weeks or months after their 

 formation. No doubt many changes in the living or non-liv- 

 ing parts of the organism fall under this head. 



Seeds in dry storage lose their power to germinate grad- 

 ually — some even after a year and others only after a cen- 

 tury and a half. This is likely due to slow coagulation of em- 

 bryo proteins (32). Seeds of Amaranthus retroflexus will not 

 germinate when harvested, but will do so after a month or 

 two of storage under uniform conditions. This is a result of 

 spontaneous ageing changes in the gels of the seed coats. Such 

 ageing changes have also been observed in spores. Heating 

 the oat coleoptile to 39 °C for one hour lowers the rate of 

 photo-perception at 20°C fourfold. After four hours at 20°C 

 the old speed is regained. This recovery has been interpreted 

 as a matter of hysteresis in cell colloids rather than elimina- 

 tion of poisons formed at the higher temperatures, although 

 the latter interpretation is possible The main virtue of classi- 

 fying some of the spontaneous changes in the organism under 

 the term hysteresis is not that it furnishes in itself an explana- 

 tion of them. It takes these problems out of their connection 

 with vital qualities and places them on the basis of a colloidal 

 substratum capable of physical and chemical study. 



Protective colloids are colloids of the hydrophyllous type 

 which have the character of forming a film about the particles 

 of suspensions or suspensoids and preventing their fioccula- 

 tion. Blood serum often bears uric acid far above the satura- 

 tion point. Albumins of the serum of the blood acting as 

 protective colloids keep the droplets of uric acid in suspension. 

 The droplets vary in size from amicrons to microns, depending 

 upon the degree of supersaturation. The high content of cal- 

 cium phosphate in milk is probably explained on a similar 

 basis. Gall stones and bladder stones are in part due to short- 



