:)4 



Icniltcraliirt' iinisl he ciitii'cly modified. AVliicli is llie 

 lowest Icniperature reaelied, liow long the material has 

 been at that temi)eralnie, and even how mnch ice has been 

 formed, become factors of secondary importance if death 

 results from a mechanical injury during thawing. 



Becquerel (19o2b) investigated the action of the tem- 

 perature of liquid gases on the tuberous roots of some 

 RauuncuJaceae. In preliminary experiments he found 

 that the roots can be dried in the air for 6 months or in a 

 vacuum for 2 montlis without losing their ability to pro- 

 duce new si)routs when remoistened. The roots, dried in 

 the air and in a vacuum, withstood an immersion of 18 

 days in liquid nitrogen ; the roots, dried and subsequently 

 soaked so as to re-imbibe respectively 45, 98 and 160 per 

 cent of their previous water-content, died. 



Lipman (1936b) immersed in liquid air for 50 hours 

 sealed tubes containing protonemata of 8 genera of 

 mosses, previously dried in a vacuum over sulphuric acid. 

 No injury resulted from the treatment, growth was nor- 

 mal and a microscopic examination revealed healthy cells, 

 and chloroplasts in a good condition. The author pub- 

 lished photographs of the plants grown from the exposed 

 protonemata. 



According to Becquerel (1932c), sprouting seeds of 

 ifheat, rye, lucern and Helianthus, which can be dried in 

 a vacuum and I'evived, do not suffer from exposure in the 

 dry state to any low temperature. The material, consist- 

 ing of seeds with radicles no more than 10 mm. in length, 

 w^as first air-dried; then it was desiccated in a vacuum of 

 10 ' mm. of mercury in presence of barium oxide ; finally, 

 it was put for 18 days in li<iiiid nitrogen. Most of the 

 rootlets could be revived after this treatment. Some 

 specimens were immersed in liquid helium for 9 hours and 

 stayed one hour at 1.84° K. in a vacuum of 10 ' mm. of 

 mercury, without suffering any injury. 



SECTION ir. ANIMAL MATERIAL 



1. Blood. To study the action of low temperatures on 

 white blood corpuscles, Schenk (1870) placed the blood of 



