BIOLOGY. 279 



re-communication of motion to the particles of water. Nature 

 produces the state called hybernation by a similar simple process, 

 causing inertia by cold and recovery by heat. It will be an in- 

 teresting study for the comparative anatomist to discover why 

 hybernating animals come so readily under the influence of cold; 

 there must either be some peculiarity of construction which en- 

 ables the cold to reach their nervous centres, or the nervQus cen- 

 tres themselves must be specially susceptible to the influence of 

 cold. 



When we have crystallized the water of the nervous matter by 

 freezing, we have reduced it from activity to inertia, and have de- 

 prived it of the power to maintain what is called life ; when heat is 

 applied, the tissues in the frog are so thin and such good conductors 

 of heat, that the nerve substance is immediately acted upon, and 

 the water becomes fluid. But, in warm-blooded animals, evolv- 

 ing and requiring more heat, their natural non-conducting tissues 

 and coverings retain their heat, and at the same time prevent them 

 from directly taking up heat sufficient to restore instantly the lost 

 heat of fluidity ; hence, in chilling their nervous centres, the oper- 

 ation must be so limited as not absolutely to stop respiration and 

 circulation ; some spark of their fire-producing apparatus must 

 remain, or the apparent death will be real. In hybernating ani- 

 mals this is the secret of their recover}^ — the fire never entirely 

 goes out. 



While similar functional disturbance of the nerves is produced 

 by cold, alcohol, or heat, there is this essential diff'erence to be 

 noted : if the nerve be solidified by cold, it will quickly regain its 

 function under the influence of heat ; if the nerve be solidified by 

 alcohol, it will slowly and imperfectly regain its function ; while, 

 if it be solidified by heat, it will, as far as our present knowledge 

 extends, be destro^'ed in regard to function altogether. 



In addition to previous researches, Dr. B. W. Richardson, in a 

 paper presented to the British Association at the Norwich meeting 

 (1868), dwelt on the question whether frogs, and other frozen 

 animals, respire during insensibility, which he decided in the 

 negative. In proof of this, he said that animals so treated could 

 be placed without harm in gases which would not support life, 

 such as nitrogen and hydrogen, and could be recovered at the 

 precise moment of recovery from the frozen state when respiration 

 was recommencing. The gradual return of heat was a pure restor- 

 ative, and the facts went toward the explanation of many disputed 

 accounts of freezing. 



In relation to the effects of freezing the brain on the circulation, 

 he show^ed that in warm-blooded animals the reduction of the tem- 

 perature of the brain produced a gradual slowness of the circula- 

 tion, and, when the freezing was carried to the base of the brain, 

 intermittence of the heart's action followed, if the operation were 

 continued, by the entire cessation of the heart's movement, — a 

 point of great practical importance, as indicating the influence of 

 the brain on the heart. Whenever the brain was reduced in. 

 physical power, as from great fatigue, or shock, or anxiety, irreg- 

 ular action of the heart was almost the necessary result. Most 



