6 VBTEEINAEY TOXICOLOGY 



tion, arsenic acid is saturated and is less poisonous than 

 arsenious acid, which is unsaturated, and Bhrlich's re- 

 searches tend to prove that a reduction from the pentavalent 

 arsenic to the trivalent arsenious stage is a necessary 

 precursor to toxicity of the arsenic compounds; the 

 unsaturated hydrocarbon acetylene in distinction to the 

 saturated ethane is poisonous ; hydrocyanic acid is more 

 unsaturated and more toxic than the sulphocyanides ; the 

 alcoholic compound betaine is far less toxic than the 

 unsaturated and more reactive but similarly constituted 

 aldehyde muscarine. 



3. Among organic compounds similarity of type com- 

 monly denotes similarity of effects, which, however, grow 

 less as complexity increases in a series of compounds. 

 Thus the alcohols resemble one another, the lower being 

 more active than the higher, and similarly phenols show 

 general likeness to one another. But there are anomalies ; 

 e.g., sulphonals containing only ethyl groups lack the 

 hypnotic effect of those containing the analogous methyl 

 group. 



CONDITIONS GOVERNING THE ACTION OF POISONS. 



A very large number of factors determine the action of a 

 poison in a given case of which the more important are— 

 Absorption, distributioji and accumulation in the organs, and 

 elimination. Minor factors are the species, age and idiosyn- 

 eracy of the subject. A manifest condition precedent to all 

 is the administration of ai sufficient quantity, the toxic or 

 lethal dose. 



Absorption. — The absorption of a poison depends : — 



1. On the physical nature of the poison. 



2. On the channel of absorption. 



1. Before absorption, which requires the formation of 

 a solution, can occur, it is necessary that the poison be in a 

 soluble and absorbable form when given, or that it becomes 

 modified so as to fulfil these conditions after administration. 



