CHEMICAL CONSTITUTION AND PHYSIOLOGICAL ACTION. 155- 



in which, although present as pentads, they are easily reduced by subtraction 

 to the state of triads. 



In reference to this, we cannot avoid referring to a very remarkable passage 

 in Bunsen's admirable paper on kakodylic acid. After describing the experi- 

 ments by which he proved the inert character of this acid, he says, '' Gehen wir 

 auf den Grund dieser unerwarteten Erscheinung zuriick, so bietet sich dafiir nur 

 in der Annahme eine Erklarung dar, dass die Verbindungsweise des Arseniks 

 im Kakodyl eine andere ist, als in seinen unorganischen Verbindungen. lndem 

 es darin aufgehort hat, fur sich einen Angriffspunkt der Verwandtschaft zu bilden, 

 hat es zugleich seine Reaction auf den Organismus verloren." ( Annalen, vol. xlvi. 

 1843, p. 11.) While it is plain that Bunsen does not here refer to the different 

 degree of saturation of the arsenic in arsenious and kakodylic acids, both because 

 the whole theory of saturation is of a much later date, and because he makes no 

 distinction between the mode of combination of the arsenic in those compounds 

 in which kakodyl is monad and arsenic triad, and those in which kakodyl 

 is triad and arsenic pentad, he points out in an exceedingly clear manner the 

 striking coincidence of peculiar chemical constitution and peculiar physiological 

 action in the case of kakodylic acid. 



While, however, the cases mentioned incline us to believe that physiological 

 activity is related to condensation, the occurrence of saturated substances, such 

 as alcohol, corrosive sublimate, and oxalic acid, having a well marked poisonous 

 action, and of condensed substances, such as benzoic acid and salicine, which 

 are comparatively inert, shows that condensation is not the only condition of 

 physiological activity. There can, at the same time, be little doubt that if the 

 effect of condensation were discovered and eliminated, the other conditions might 

 be much more hopefully sought for. 



Under these circumstances, we turned our attention, in the first place, to the 

 effect of chemical addition in altering the physiological action of the natural 

 alkaloids. We were led to do so, partly by a consideration of the ease with 

 which, by means of iodide of methyl, the nitrogen of nitrile bases can be 

 rendered stably pentatomic, and partly by the hope, grounded on the obser- 

 vations of Stahlschmidt in reference to the salts raethyl-strychnium and 

 methyl-brucium, that we should obtain marked changes of physiological 

 action. 



The great majority of natural alkaloids belong to the class of nitrile bases, 

 that is, they contain one or more atoms of triatomic nitrogen directly united to 

 carbon by three bonds. This nitrogen atom (or, in the case of poly-acid bases, 

 atoms) can become pentatomic, as in the formation of salts ; thus in the forma- 

 tion of hydrochlorate of morphia the nitrogen takes up H and CI, thus becom- 

 ing pentatomic, united by three bonds to carbon, by one to hydrogen, and by 

 one to chlorine. But by this change it is not rendered permanently or stably 



VOL. XXV. PART I. 2 R 



