55 



tritons, frogs or turtles in a shallow glass and set this on 

 a freezing mixture; the temperature \vas recorded by a 

 thermometer immersed in the blood. The white cells 

 cooled to 0°, -3°, -5°, or -7° for a short time, retained 

 their vitality and resumed amoeboid movement when the 

 temperature was again raised. If the blood was kept 

 for several hours at low temperature, movement was only 

 seldom resumed ; thus, a specimen kept for 8 hours at - 2° 

 to - 3°, did not resume its activity. The white blood cells 

 of the warm-blooded animals, especially of the rabbit, 

 retained their vital properties after exposure to - 3°, only 

 if the time of exposure was not more than 10 to 15 min- 

 utes. In Schenk's experiments the blood corpuscles were 

 apparently never congealed. 



Pouchet (1866) reported that the red blood cells were 

 considerably altered by congelation. Frog's blood was 

 allowed to drop into a dish cooled to -15°. After thaw- 

 ing, the iniclei were found free in the plasma. In other 

 experiments, he froze entire animals such as frogs, toads, 

 an eel, a young cat, etc., and observed that the blood cor- 

 puscles were crenated and reduced in size. From these 

 observations he developed the theory that the damage 

 done in the body of an animal by freezing was in direct 

 ratio to the number of blood cells injured. 



2. Embryonic Tissue. Simonin (1931) subjected frag- 

 ments of embryonic tissues of mouse, rat or ox, to tem- 

 peratures from 0° to - 15°, in boxes immersed in a freez- 

 ing mixture. He could obtain some growth in culturing 

 these tissues after they had been at 0° for 20 days or at 

 - 5° for 5 days, provided no ice had been formed in them; 

 - 15° was always lethal in a short time. Nerve cells and 

 liver tissue were most sensitive, while heart, lung, and 

 intestine tissue showed a greater cold resistance. 



Gaylord (1908) observed that growing epithelium from 

 young mice embryos was killed after immersion in liquid 

 air. 



The embryos of the birds were always found more re- 

 sistant to low temperatures than the adults. But almost 



