8 CHEMICAL AGENTS AND PROTOPLASM [Ch. I 



lytic poisons ; the process -which they inaugurate being known 

 as catalysis (apparently produced by mere contact). 



First will be considered the laws of relation between molecular 

 composition and strength of action. We may begin with the 

 methan series. This series, which has CHg — as its base, runs 

 as follows : — 



C2H6 

 CgHs, etc. 



In the members of this series, the poisonous action increases 

 up to a certain limit, with the number of O atoms ; above that 

 limit the compounds are more stable and are more indifferent ; 

 e.g. paraffine (C^iH^^ to Cg^Hgg). 



Beginning with methan, CH^, we find this substance — marsh 

 gas — innocuous when mingled with air. As the H atoms become 

 replaced by one or more chlorine atoms, the poisonous qualities 

 increase., — 



CH3CI is slightly aneesthetic, 



CHCI3 = chloroform, 



CCI4 is very dangerous, stupefying involuntary muscles. 



If the H atoms are replaced by any other halogen, — e.g. I, — 

 anaesthesia is produced among some Vertebrates. Thus, 0.6 to 

 1 grain of CH2T2 kills a rabbit. 



In ethan (CgHg) also, when CI replaces H, the substance be- 

 comes a more active poison ; e.g. CjHjClg, methal chloroform, 

 acts like chloroform. 



Also, among the sulphur hydrocarbons we observe the same 

 fact of increase of poisonous action with increase in the number 

 of CI atoms to the molecule ; thus, — 



sulphur ethyl, C2H5— S— CaHj is a weak poison, 



monochlorsulphurethyl, G2H5— S— CjH^Cl is a stronger poison, 

 diehlorsulphurethyl, C2H4CI — S — C2H4CI is a very powerful poison. 



In the more complex sulphonic hydrocarbons of the methan 

 series, where the alkyls CHg-, CgHj-, etc., are introduced, 

 the rule holds that the more atoms in the alkyl the more active 

 the substance as a poison ; thus, — 



