251 



have a narrow freezing range. For example, a concen- 

 trated solution of dextrin freezes only between about - 1° 

 and -9. Similarly the substance of some types of pro- 

 toplasm might have a very narrow freezing range. If, 

 then, the degree of subcooling is such that the freezing 

 range can easily be traversed, the formation of ice is 

 avoided. 



As to the organisms of the first group, those which 

 can be dried, they resist not only cold but almost any 

 injurious agent w^hen they are in the dry condition. Such 

 a general resistance is again attributed to the absence 

 of water. But evidently the ability to support without 

 injury the removal of water is due to some intrinsic 

 property characteristic of some given types of proto- 

 plasm. 



A priori it seems that the resistance to cold could be 

 attributed directly to this intrinsic property rather than 

 to the actual absence of water and consequent absence of 

 ice. But experiments have shown that most of the desic- 

 cable organisms are killed when frozen without being 

 previously dried. To mention one instance, Adams (1905) 

 found that seeds which contain more than 12% water may 

 be killed by freezing, while if they are dried to a fur- 

 ther extent they remain uninjured. These experiments 

 clearly speak in favor of the theory of the actual ab- 

 sence of freezable water as the cause of the resistance to 

 extreme cold in desiccable organisms. 



In the instance given, 12% of the weight of the seeds 

 would then be unfreezable water. This proportion, it 

 might be remarked, is low when compared to the 34.5% 

 water content which has been found by Moran (1926) to 

 stay unfrozen at any low temperature in gelatin gels. The 

 quantity of water which, in several colloids, cannot be 

 unbound by crystallization forces is considerably higher 

 than is usually thought. 



Coming now to the explanation of the survival of pro- 

 toplasm treated by the rapid cooling and rewarming 



