P0IS0K3j^^^.-__;^ 185 



> OF THE 



NIVERSITY 



CHAPTER II {Continued), 



Addendum 1. — Poisons. 



In tbe consideration of matters which act deleteriously 

 upon the animal system some difficulty is experienced in 

 defining the term poison. For if we accept the common 

 interpretation of the term, anything taken by an animal 

 which causes sickness or death, we are at once faced by 

 the difficulty that certain parasites and mechanical impedi- 

 ments to passages, as calculi or a turnip in the oesophagus 

 may be thus considered, and any alimentary matter would 

 thus be a poison if taken in sufficient quantity or in an un- 

 prepared state. Dr. Taylor's definition is about the best 

 with which we are acquainted : " A poison is a substance 

 which, when absorbed into the blood, is capable of seriously 

 affecting health or of destroying life.^^ But it seems to 

 exclude certain corrosive agents which we must consider 

 as poisons. A poison is any substance which, when intro- 

 duced into the body in moderate doses, is capable of 

 producing serious disorder or death, without acting me- 

 chanically or by vital growth and propagation. We thus 

 exclude, on the one hand, impactions of foreign bodies, on the 

 other, parasites, and especially bacterial organisms, which 

 are the active principles of the majority of animal poisons 

 (so-called) or preferably "virulent^^ matters. A considerable 

 analogy exists between poisons and medical agents, and 

 no small difficulty will be found in distinguishing one from 

 the other. This arises from the fact that there is no true 

 distinction but that of degree in action ; every therapeu- 

 tical agent has a maximum dose, which varies according to 

 the special circumstances of each case, and if this be 

 exceeded will act as a poison. Thus, our most powerful 

 poisons, when given in moderate doses are our most useful 



