59 



drop of liquid paraffin. The coverslip with the hanging 

 drop was mounted on a chamber on the stage of the micro- 

 scope, and the temperature ascertained with a thermo- 

 couple inserted into the drop near the tissue. It was 

 found that muscle fibers could be subcooled at -6.5° for 

 2 hours or at - 15° for 3 hours without losing their power 

 of contraction. Surface freezing, induced by touching 

 the fiber with an ice-tipped pipette, occurred at - 1.2°, and 

 after a stay of about 15 hours at - 1.2° to - 1.3°, a slight 

 contraction could still be produced. Internal freezing 

 occurred at - 1.6°, but fibers in which such freezing was 

 complete were always found to be dead on thawing. 



Heubel (1889) studied the effect of freezing on the 

 frog's heart in situ, as follows. He directed a stream of 

 ether from an atomizer upon the exposed, ligated and 

 therefore relatively blood-free heart, thus freezing it hard 

 through and through. The operation lasted 20 to 30 

 seconds. When the ligature was removed and the blood 

 forced into the heart, it soon started to beat and, shortly 

 after, it functioned normally again. Hearts subjected to 

 the cooling action of the ether for more than 1 minute 

 could never be revived, nor could hearts w^hich were 

 exposed for 10 or for 17 minutes (1 experiment in each 

 case) to an air-temperature of -18°. 



According to Cameron and Brownlee (1913), excised 

 frog's hearts, placed in test tubes immersed in freezing- 

 solutions, recovered after having been frozen at tempera- 

 tures of -2.5° to -3° for two hours, but not after treat- 

 ment at lower temperatures. Recovery consisted in a 

 reestablishment of the beat after it had stopped. These 

 authors made about 25 determinations of death tempera- 

 tures on excised hearts. 



Britton (1924) mentions a sJiate exposed for 16 hours 

 to -20° and solidly frozen, the heart of which resumed 

 its beat after thawing, though the fish did not recover. 

 The author states that the heart of the skate can be solidly 

 frozen for several hours and recover. 



5. Nerve Tissue. Biihler (1905) observed that, when 

 the temperature of an isolated frog's nerve (Ischial of 



