INTEODUCTION 



DEFINITION OF A POISON. 



A poison may be defined as a substance which, when 

 introduced into the body in relatively small amount, acts 

 deleteriously, and may cause death. 



It is at once evident that a hard and fast definition, here 

 as in most things, is almost impossible. Kestrictions — 

 many based on scientific grounds, but most on those of 

 common sense — at once suggest themselves. The forcible 

 introduction of a bullet, or a knife- blade, or the mechanical 

 lesions of powdered glass^ cause death. Though not scien- 

 tifically called a poison, the latter substance would be held 

 equivalent in the eyes of the law. The great majority of 

 the poisons are also drugs, and, as Cushny well expresses it, 

 ' some bodies may, in fact, be remedies, foods, or poisons, 

 according to the quantity ingested and the mode of 

 application.' 



The following important restrictions and limitations to 

 the foregoing definition are accordingly suggested : 



1. A poison in sublethal quantities exercises a specific 

 effect on the organism, interfering with the normal action 

 of some one or more particular group of cells. 



This distinction appears necessary, for it is desirable to 

 withdraw from the category of poisons, properly so under- 

 stood, certain (possibly all) foods. It is distressing to hear 

 that, on the strength of the bad results of injudicious feed- 

 ing, or over-feeding, certain foodstuffs are given the grave 

 designation of " poisonous." Yet we know that bad dieting, 

 and especially the irrational use of a new food, may earn it 

 an evil, but often undeserved, reputation. 



2. A poison differs from a bacterial toxine in that a 

 poison, as here understood, never gives rise on long con- 

 tinual sublethal dosage to the formation of an anti-body in 

 the blood serum. This distinction seems quite sharp, 

 although of course the bacterial toxines — e.g., of diphtheria 

 or tetanus — may be correctly said to be poisonous. More- 

 over, the phytotoxines (ricine, crotine, abrine) and zootoxines 



