80 Tait 



ledo-e of this subject is due, sliowed that fishes which had been cooled down 

 in a block of ice to —15° C still remained alive after careful warming, 

 although others similarly treated could be pounded like ice into powder. 

 After a temperature of — 20° C the fishes were found to be dead. Frogs, 

 again, withstood a temperature of — 28° C. 



The exact temperature at which freezing of frog's nerve occurs I have 

 been unable to determine. Boycott (5), who also records some experiments 

 on freezing of nerve, was inclined to place the freezing-point somewhere 

 about —7° C. With my apparatus, which probably gave a more exact 

 determination than his, I found that freezing occurs at a temperature 

 somewhat higher than this, viz. between —3° and —5-5° C. 



To study more exactly the changes produced in nerve by means of 

 freezing, it seemed better to freeze a minute length than to freeze a longish 

 portion. By means of a piece of glass-tubing with an hour-glass constric- 

 tion in the middle, on to which the nerve suspended between two pairs of 

 electrodes could be lowered, it was possible to freeze a very short length of 

 the nerve by running cold alcohol through the tube, and to subsequently 

 thaw it again by running in warmer fluid. The outside diameter of the 

 constricted part of the tube was 2 mm. The alcohol was cooled by means 

 of an ice and salt cooling mixture, consequently the temperature of the 

 frozen part of the nerve might vary from the freezing-point right down to 

 within a few degrees of — 22° C. The vessels containing the supply of cold 

 fluid and of warm fluid respectively were connected with the glass tube by 

 means of a three-way stop-cock. A small screw clamp connected to a piece 

 of rubber-tubing at the further end made it possible to regulate the rate of 

 flow and thus to roughly graduate the temperature. The two pairs of 

 stimulating electrodes on which the nerve was suspended were connected 

 by means of a Pohl commutator, from which the cross wires were removed, 

 to a standard Kronecker induction coil, in the primary circuit of which 

 was placed a small accumulator charged to 4J volts. By means of these 

 electrodes the nerve could be stimulated either centrally or peripherally 

 to the cooled portion. 



I. Changes during Freezing. 



It is difficult to determine the exact cause of the muscular twitchings 

 that accompany freezing of the nerve. Prolonged observation showed that 

 by the time the muscle twitchings began the whole of the small portion of 

 nerve lying over the cold tube was already opaque in appearance. This 

 might indicate that the nerve is frozen right through before twitchings 

 occur ; but, on the other hand, the white appearance may be due to deposi- 

 tion of hoar-frost from the atmosphere before the salt solution inside the 

 nerve has reached its freezing-point. The generally accepted idea is that 

 the twitchings and subsequent loss of conductivity in the nerve are due to 

 mechanical compression owing to the expansion of the water-substance in 

 the nerve during freezing, and it has been shown (6) that mechanical 



