Dr. Davy on the Congelation of Animals. 



251 



to repeat the experiments on the leech, and to extend them to some other 

 animals. They were begun at Oxford in May, in the laboratory of Pro- 

 fessor RoUeston, with the kind assistance of Mr. Edward Chapman and 

 Mr. Robertson ; and since then, in the following month, they have been 

 continued at home in Westmoreland. 



At Oxford the trials were made on leeches and frogs ; at home, on 

 these animals, and on the toad and some insects. The freezing mixture 

 was made of pounded ice and common salt ; the temperature by it was 

 commonly reduced to below 10° Fahr., or at times so low as 2° or 3°. The 

 results obtained were briefly the following : — 



1. A leech was exposed to the mixture in a small glass tube just large 

 enough to hold it, using the tube for stirring the mixture. Taken out 

 when perfectly rigid and hard, and gradually thawed, it showed when 

 punctured a faint indication of irritability ; there was a just perceptible con- 

 traction of the part punctured, the oral extremity, and nowhere else. It 

 did not revive. 



2. Another leech was similarly exposed, but for a shorter time. When 

 divided by an incision, it was found not frozen throughout. When punc- 

 tured, it showed marks of irritability in a slight degree stronger than the 

 preceding : it soon died. 



3. Two leeches were similarly treated at home, and for a somewhat 

 longer time ; the temperature reduced to 3°. These, when gradually 

 thawed, one exposed to the air, the other left in the mixture, showed no 

 marks of revival ; but they retained a certain elasticity, so that when bent 

 they shortly recovered their former attitude, after a manner somewhat re- 

 sembling a vital movement ; but inasmuch as they did not respond by the 

 slightest contraction to puncture, it may be inferred that the movement 

 was not vital. They resisted putrefaction for many days. 



4. A frog in a thin glass vessel was kept in the mixture about a quarter 

 of an hour. It was very rigid when taken out ; thawed, no part on punc- 

 ture afforded any indications of life ; watched two or three hours it proved 

 to be dead. 



5. The heart of a frog, removed immediately after decapitation, whilst 

 still pulsating, was subjected to the freezing mixture in a small glass tube. 

 After having been frozen, on thawing it remained motionless, even when 

 punctured. It had been kept in the mixture only a few minutes. 



6. The inferior extremities of a frog kept extended by a bandage and 

 thus introduced into a glass tube, were submerged in the mixture, the body 

 of the frog being held in the warm hand ; taken out after some minutes 

 they were quite hard and motionless, whilst the body and upper extre- 

 mities did not appear to be affected. It moved about, dragging the lower 

 extremities as if they were dead. In about four hours it recovered the use 

 of its femoral muscles ; on the following day the use of the muscles of the 

 legs ; the day after it was able to bend and extend these limbs ; but there 

 was no proof that its feet had recovered sensibility. On the fourth day it 

 was found dead. 



