121 



5. Protoplasm. Chambers and Hale (1932) induced 

 freezing in amoeba proteus by seeding the supercooled pro- 

 toplasm with an ice-tipped micromanipulator needle at a 

 temperature of - 0.8° and below. 



Gehenio and Luyet (unpublished work) determined the 

 freezing point of the living plasmodium of the myxomycete 

 Physarum poli/cephalum. Some 5 cc of protoplasm col- 

 lected from agar cultures were used in each determination. 

 The values found in 7 specimens average -0.17°. 



6. Tissues. The determination of the freezing points of 

 living tissues by any of the methods used involves an ele- 

 ment of uncertainty. Ice-seeding, to prevent subeooling, 

 or at least to prevent a too considerable degree of subeool- 

 ing, is an essential procedure for any accurate freezing- 

 point determination. But ice-seeding through cell w^alls 

 is not always efficient ; only some cells might freeze after 

 seeding or spontaneously, others not ; the number of cells 

 frozen might not suffice to bring the temperature of the 

 subcooled object up to the freezing point. On that basis 

 one should, perhaps, question most of the results obtained 

 for the freezing points of living tissues. 



Collip (1920b) determined the freezing point of the pulp 

 obtained by grinding various tissues of the dog. He found 

 values varying from -0.74° to -0.87° for the heart, the 

 spleen and the lungs, -0.91° for the liver, and -0.76° for 

 the brain. 



Jensen and Fischer (1910) obtained, for the frog's 

 muscle, in the living state, freezing points varying from 

 - 0.46° and - 0.53°. 



Cameron and Brownlee (1913) give -0.44° as the freez- 

 ing point of an entire frog exposed to the freezing tempera- 

 ture with a thermometer in its stomach. 



Living and Dead Tissues. ^liiller-Thurgau 

 (1886) noticed that living tissues have a lower freezing- 

 point than dead ones, that is, than tissues killed by a first 

 freezing. He found - 0.98° and - 0.55°, respectively, for 

 living and dead potato tuber, and likewise, - 0.8° and - 0.4° 

 for living and dead Phaseolus leaves. For the determina- 



