67 



rious solutions conlaining surface active substances. About 

 30 "/o of the total nitrogen adsorbed could be dissociated 

 from the blood coal. The displaced substances did not seem 

 to possess any sli'iking effect on the cell-activity. 



The fact thai direct chemical tests are not yet available 

 to determine the chemical nature of the so-called growUi 

 promoting substances, leads us to find other indirect methods 

 of studying them. 



As indicated before, 1 got an impression that it might 

 probably be explained that individual definite protein or 

 substances do not exist, which alone are responsible for 

 the growth promoting power, but the activity of llie tissue 

 juice might very well be the result of phj'Sico-chemical inter- 

 actions in the colloidal system. The proteins in the body 

 juices represent a polydispersoid system and its physical 

 properties, surface energy, viscosity, electrical charge and 

 osmotic pressure, are \evy much influenced by the active 

 reacting substances, which so far have been used for the 

 separation of the supposed more or less definite compounds. 



We know now as facts, that the embryonic tissue juice 

 freshly prepared, has the ability to maintain life of tissue 

 cells indefinitely outside the organism ^^) i*^^). We know also 

 from the experiments that merely by storing the tissue juice 

 for some time, even in the cold, it loses much of its growth 

 promoting power; it is likewise known, that shaking "'*) the 

 tissue juice or heating it to 56 ^ C. greatly suppresses its 

 power. These facts could very well be explained by the as- 

 sumption that a change in the colloidal system takes place 

 of a more physical character. Colloidal solutions differ from 

 the true solutions only in the sizes of particles or mole- 

 cules. The protein solutions are probably true solutions, but 

 their molecules are so large that their physical properties 

 very closely approach those of the colloids. We know that 

 colloidal solutions of the simplest kind as ordinary metal 

 sols for instance, are rather unstable in function of time 

 and still more in function of temperature. Changes are 



5* 



