108 BENEFICIAL ACTION OF CERTAIN POISONS . HARRIS. 



as they act specifically on the neuroplasm, but not nearly so 

 directly on the enzymes of tissue-respiration. 



5. Substances which both immobilize the biogens of 

 neuroplasm and also retard the velocity of action of one or 

 other of the enzymes of internal respiration, namely reduc- 

 tase and oxidase, but do not destroy secretion-enzymes. 



Examples of these are chloroform, ether, alcohol, quinine, 

 KCN, AS2O3. 



6. Substances which act injuriously on all the three, 

 the biogens, the endo-enzymes, and the secretion-enzymes. 

 Examples: — Mercuric chloride, silver nitrate, and all salts 

 of heavy metals when in sufficient concentration. Thus 

 Uranium salts as weak as 0.0001% retard ptyalin, and in 

 solution no stronger than 0.008% completely inhibit it. 



