1888.] on Poisons and Poisoning. 225 



Why (you ask) does that kill ? I cannot tell you. It is the highest 

 form of knowledge to see the limits of positive knowledge, and to 

 make that the starting-point for fresh inquiry. 



From what I have said, it will be evident that my object has been 

 to trace toxic energy to the chemical action of poisons on living 

 tissues or fluids. The phrase " physiological action " must not be 

 understood as implying any theory re modus operandi. There is a 

 danger lest the phrase " physiological action " should be employed, or 

 regarded, as explanatory. It no more explains (be it remembered) the 

 action of certain drugs on the living body than the word catalysis 

 explains fermentation. 



There naturally follows on what I have said respecting this 

 chemical action of poisons, the following important question : — 



Given knowledge of certain properties of the elements, such as 

 their atomic weights, their relative position according to the periodic 

 law, their spectroscopic characters, &c. ; — or given knowledge of 

 the chemical composition, the molecular constitution, together with 

 the general chemical and physical properties of compounds, in other 

 words, given such knowledge of the element or compound as may be 

 learnt in a laboratory — does such knowledge afford any clue whereby 

 we may predicate the probable action of the element or of the com- 

 pound respectively, on the living body ? 



1st. Let us limit our attention to ike elements. 



The starting-point of this inquiry was the toxic properties of the 

 metals. The work of Blake (1841) in this direction was afterwards 

 extended by Eabuteau (1867). Their observations led them to the 

 general conclusion, that "the physiological activity of the metals 

 increased with their atomic weight." I'his broad general statement 

 was modified at a later period by noting that the reverse was the case 

 with certain groups of metals. Thus potassium (39) is more poisonous 

 than sodium (23), and barium (137) more poisonous than calcium 

 (41). These facts led Eabuteau to the conclusion, that any com- 

 parisons of toxicity must be limited to the metals belonging to the 

 same group. Husemann and Eichet, however, pointed out that 

 even this rule did not hold good, seeing that lithium having an atomic 

 weight of 7, was far more poisonous than either sodium or potassium. 



Experiments on the metals were further conducted by Eichet with 

 the metallic chlorides. Grain by grain, at intervals of forty-eight 

 hours, he added the chlorides to water in which he kept fish of a given 

 kind. He then recorded the maximum strength of the solution of the 

 metallic chloride in which these said fish would live for forty-eight 

 hours. The conclusion at which he arrived was that the limits of 

 the toxicity of a metal bore no relationship either to its atomic 

 weight, or to any other chemical or physical characteristic of the metal. 



Bouchardat and Stewart Cooper, in a similar manner, experimented 

 with the non-metals. Selecting the haloid group of elements, they 



