74 COLLOIDS IN BIOLOGY AND MEDICINE 



freshly poured gelatin cylinders reach a practically constant modulus 

 of elasticity at the end of three to four hours. This accords with the 

 fact observed by F. STOFFEL, that crystalloids diffuse more rapidly 

 in quickly chilled than in slowly chilled gelatin, and that this differ- 

 ence disappears after several days (see p. 54). 



At the outset we spoke of the "life curve of colloids," of " aging 

 phenomena," "death," "individual properties," etc., and it might 

 appear that these are only similes borrowed from the organized 

 world. In my opinion the relationship is closer, and I believe that 

 we may obtain a more profound understanding of the phenomena of 

 Life (so unintelligible to us) by a study of such phenomena in colloids. 



Aging has hitherto been considered, for the most part, a purely 

 biological phenomenon. In my opinion, we may attack the problems 

 with the methods of exact science, if we could but separate two 

 groups: the organs (cell groups), which constantly renew themselves, 

 from those which are lasting. We would, d priori, expect changes 

 in the latter similar to those observed as aging phenomena in col- 

 loids. We saw that a rapidly chilled gelatin was at first easily pene- 

 trable for crystalloids, but that with time its resistance increased. 

 We may, therefore, assume that in young organs (fresh membranes) 

 the exchange of matter by diffusion proceeds more rapidly. The 

 decrease in elasticity, one of the most characteristic phenomena of 

 aging, may be measurably followed in aging gelatin. In fact it has 

 been shown that for the vital staining of nerves with methylene blue, 

 young animals are more suitable than old ones. With aging there 

 occurs shrinking, which begins already in intrauterine life. In the 

 third month of human fetal life the water content is 94 per cent, at 

 birth it is 69 to 66 per cent, in adult life 58 per cent. We may say 

 in general that with aging there is a decrease in the swelling capacity 

 of the organ colloids. This holds both for animal organisms, which 

 lose water as they grow older, and for plants (dry leaves lignifi- 

 cation). 



