288 



ill ])r()t('iii coiitciil observed, l^iit this criticism does not 

 ai)i)ly to a second .uroup of exi)ei-iineiits in wliicli Gorke 

 measured the amount of ])roteiu wliich precipitated in 

 the freezing of previously extruded sap. lie found a 

 noticeable quantity of nitrogen in the precipitate of the 

 frozen specimens. From these and other experiments 

 in which it was found that the precipitation of proteins 

 in i)hints of varying cold resistance (for example, mus- 

 tard leaves and spruce needles) requires either a dif- 

 ferent low temperature (-3° and -40° respectively) or 

 a different salt concentration (2.7 N and over 5.4 N NaCl 

 respectively), Gorkc^ concludes that the specificity ob- 

 served in the behavior of plants exposed to cold de- 

 pends on the ease of precipitation of the proteins. 



Xord (1934) remarks that if death is characterized by 

 the transition from a clear, homogeneous protoplasm to 

 a coarse, microscopically heterogeneous material, it is 

 natural to think that such a transformation corresponds 

 to the freezing point of some aqueous solutions and to 

 the coagulation point of some proteins. Since his inves- 

 tigations on the action of freezing on various suspensions, 

 colloidal solutions, and enzymes have resulted in the 

 conclusion that the size of the colloid particles is modi- 

 fied by crystallization of water, he correlates death with 

 changes of this kind. 



Mirsky (1937a and b), who observed that extracted 

 myosin coagulates by freezing or drying and that myosin 

 within the nniscle coagulates on being rehydrated after 

 having been dried, postulates that death by freezing, in 

 the muscle, results from a coagulation or aggregation of 

 the myosin molecules caused by some change during 

 freezing or during the reimbibition of water. 



Harvey (1918) found a higher hydrogen ion concen- 

 tration in the sap of frozen than of unfrozen plants. 

 Whether this ionic dissociation is an immediate effect 

 of freezing or whether it results from various interme- 

 diate transformations, it is im])ossible to say. 



