50 CHEMICAL AGENTS AND PROTOPLASM [On. I 



plasm itself, but of the thermogenic substances stored therein 

 (sugar, yolk). After these have been consumed in starvation, 

 or when the organism is subjected to the action of oxidizing 

 poisons, the molecules of the protoplasm become oxidized. 

 All protoplasm which is readily accessible must be injured by 

 the direct attacks of " active " oxygen. 



b. Salt-forming Poisons. — The facility with which an acid 

 or a base forms salts with the protein substances of the proto- 

 plasm must depend, in large part, upon the quality of the 

 protein molecules. It is well known that certain protein sub- 

 stances, such as keratin, chitin, and fibrin, are not readily acted 

 on by acids or bases, and it seems necessary to suppose that 

 some such resistant proteids are the essential parts of glands 

 which secrete these reagents. Into this group fall the salts of 

 heavy metals characterized by their extraordinary fatalness. 



e. Substitution Poisons. — This group comprises, besides a 

 few sulphur compounds, almost exclusively nitrogenous sub- 

 stances, and among these a large proportion of compounds 

 with closed chains. As many of these are indifferent to dead 

 albumen, but violent poisons to living protoplasm, it is clear 

 that the latter must contain certain extremely unstable groups 

 (amido-, aldehyde-, and keton-groups, LOEW, '80). Among 

 these poisons the relation between molecular structure and 

 poisonous action is very marked, especially in the nitro-com- 

 pounds. Thus, bodies containing H united with N are poison- 

 ous in direct proportion to the number of H atoms so combined. 

 It seems probable that H so combined is very easily given up 

 to the molecules of the living substance, destroying them. 

 H in the hydroxyl radical seems also more easily parted with 

 than H joined to G. 



d. Catalytic Poisons. — Chiefly organic compounds of the 

 fat series, which have little chemical energy and produce, for 

 the most part, anaesthesia. The poisonous action seems here 

 proportional to the complexity and instability of the compound. 

 Thus, in many groups, when the alkyls CHg — , CgHg — , etc., 

 are successively introduced, the substance grows more poison- 

 ous as the number of atoms in the alkyl increases. In the 

 methan series and among sulphureted compounds the substi- 

 tution of CI for H increases the poisonous action. 



