INTEODUCTION 5 



salts with acids. A most numerous class represented by, 

 e.g., strychnine, atropine, conine, taxine, etc. 



(b) Glucosides, compounds which, by the action of dilute 

 acids or enzymes, take up the elements of water, and are 

 resolved, giving, along with other compounds, always sugars, 

 e.g., digitalin, helleborin, amygdalin, etc. 



(c) Acrid juices or resins, amorphous, faintly acid, irritant 

 substances, commonly contained in saps — e.g., of euphorbia, 

 and ranunculus. 



(d) Indefinite principles, neutral in chemical respects — 

 e.g., anemonine, cicutoxine, picrotoxine. 



(e) Essential oils — e.g., turpentines (savin), tanacetone 

 (tansy), camphor, mustard oil. 



(/) Toxines — e.g., ricine, abrine, venoms. 



{g) Cyanides, hydrocyanic acid produced in plants from 

 glucosides, but also prepared in other ways, and its salts. 



(A) Phenols, hydroxy derivatives of the aromatic or 

 benzene hydrocarbons, sometimes found in plants — .e.g., 

 tannin — but mainly encountered in the tar of coal and wood 

 distillation — e.g., carbolic acid, cresols. 



The extraordinary range and variety of chemical types 

 covered by this incomplete scheme serves to accentuate the 

 extreme difficulty of any correlation of chemical nature and 

 physiological or toxic activity. That the effects are due to 

 a chemical reaction between the agent and the cell sub- 

 stances, far from being a pious opinion, seems almost a 

 truism. Of the nature of those reactions we are profoundly 

 ignorant. So far, little has been done beyond the recogni- 

 tion of certain general correlations between activity and 

 composition, thus, for instance : 



1. Antimony, closely allied chemically to arsenic, resem- 

 bles it in its effects on the organism. 



2. In general the condition known to chemists as 

 unsaturation (i.e., the possession of unsatisfied or uncom- 

 bined valencies by a molecule, rendering it able to combine 

 directly with other substances), in comparison with saturation 

 (i.e., when all the valencies are actually in combination), is 

 accompanied by greater physiological activity. In illustra- 



