ON MATTER AND FORCE. 85 



proach to rest. Hence rest and motion may 

 be taken as the two great aims of therapeutical 

 actions. 



The two substances which perhaps I might 

 name as best showing these opposite actions, 

 are laughing gas, Np 9 ^ which, in small quan- 

 tity, rapidly increases involuntary and volun- 

 tary motion; and prussic acid, HCN, which 

 almost immediately stops all conversion of 

 energy in the heart, diaphragm, and other 

 respiratory muscles, by paralysing the excito- 

 motory ganglia in the heart itself, and by the 

 same action on the eighth pair.* 



These are some of the questions which are 

 opened to therapeutical inquiry by the doctrine 

 of the conservation of energy and the insepara- 

 bility of matter and force. 



When these questions can be answered, most 



* Some late experiments of Dr. Preyer, of Bonn, show that 

 when an animal is made for some time to hreathe oxygen, 

 and then is given a small poisonous dose of prussic acid, the 

 poison takes no effect whatever. (Die Blausaure, W. Preyer, 

 M.D., Bonn, p. 67.) 



" Prussic acid, he says, acts as if it suddenly robbed the 

 blood of oxygen. If we were able to take away from an 

 animal all the oxygen of its blood in a few seconds, then, 

 without the least doubt, we should have a perfect representa- 

 tion of poisoning by prussic acid." P. 69. 



