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V. — On the Connection between Chemical Constitution and Physiological Action. 

 Part. I. — On the Physiological Action of the Salts of the Ammonium Bases, 

 derived from Strychnia, Brucia, Thebaia, Codeia, Morphia, and Nicotia. By 

 Dr A. Crum Brown and Dr Thomas R. Fraser. 



(Read 6th January 1868, under the title " On the Changes produced by direct Chemical Addition on 

 the Physiological Action of certain Poisons.") 



There can be no reasonable doubt that a relation exists between the physiolo- 

 gical action of a substance and its chemical composition and constitution, under- 

 standing by the latter term the mutual relations of the atoms in the substance. 

 There are numerous indications of such a relation, and attempts have been made 

 to express it formally in certain cases. Thus it has been long observed, that the 

 salts of the same base have a common physiological action, and it has been 

 pointed out by Mr Blake * that, with some exceptions, the salts of isomorphous 

 bases have a similar action. A corresponding likeness in physiological action may 

 be traced in salts having the same acid, but beyond these generalisations we 

 are not aware that any approach has been made to the statement of a law con- 

 necting the physiological action of a substance with its chemical constitution. 



Some observers have endeavoured to connect physiological action with com- 

 position, looking for the cause of the peculiar action of substances in the presence 

 or proportion of particular elements. It is a sufficient answer to this to point to 

 isomeric or polymeric bodies — bodies having identically the same composition — 

 which differ totally in action, such as acetic acid (C 2 H 4 2 ), and sugar (C 6 H 12 6 ) ; 

 glycocoll (C 2 H 5 N0 2 ), and nitrite of ethyl (C 2 H 5 N0 2 ) ; or to instance kakodylic 

 acid, which is inert, although perfectly soluble, and containing more than 54 per 

 cent, of metallic arsenic. 



Examples such as these clearly show that composition alone is guite insuf- 

 ficient to explain physiological action, and that constitution must also be taken 

 into account in every attempt to connect the chemistry of substances with their 

 action on the animal body. 



The most direct way of making such an attempt would obviously be to com- 

 pare physiological action and chemical constitution in a sufficiently large number 

 of cases, and by classifying the results to deduce a law ; but, unfortunately, the 

 data which we possess are quite insufficient for this. We know, indeed, the 

 " structure" of a considerable number of substances ; that is, we know the order 



* Proceedings of the Royal Society of London, vol. iv. Jan. 28, 1841, p. 285. 

 VOL. XXV. PART I. 2 Q 



