' 154 DRS CRUM BROWN AND FRASER ON THE CONNECTION BETWEEN 



cases of change of activity produced by replacement, such as the singular inert- 

 ness of ferrocyanide of potassium and of the analogous double cyanides, as com- 

 pared with the activity of cyanide of potassium and its analogues. 



On the other hand, operations of addition, particularly where the condensation 

 diminished by the addition is intra-atomic, seem, in many cases, to produce very 

 decided change both in the kind and in the degree of the physiological activity of 

 the substance acted on. The following examples will illustrate this statement. 



Some are cases of direct and some of indirect addition, and in all of them the 

 change of structure produced is known, and there is in none of them much risk 

 of fallacy arising from the change taking place spontaneously in the animal 

 system. The first column contains the names and formulas of the substances 

 before addition, the second the atoms or groups added, and the third the names 

 and formulae of the substances produced. 



I. II.' III. 



Carbonic oxide, CO O Carbonic acid, C0 2 



Hydrocyanic acid, HCN 2H. 2 + HC1 Hydrochlorate of methylamine, CNH 6 C1. 



Arsenious acid, As 2 3 , [HAs0 2 ] (CH 3 ) 2 Kakodylic acid, AsC 2 II 7 2 * 



Strychnia, C 21 H 22 N 2 2 (CH 3 (HO)) Methyl-strychnia (hydrate), C 22 H 26 N 2 3 f 



Brucia, C 23 H 26 N 2 O i (CH 3 (HO) ) Methyl-brucia (hydrate), C 24 H 30 N 2 O. + 



It will be observed that all the substances in the first column are highly 

 poisonous, while those in the third column are either quite inert, or possess an 

 action entirely different in kind from that of the bodies from which they are 

 derived, and very much less in degree. 



A consideration of the hitherto isolated facts collected in the above table 

 leads not unnaturally to a suspicion that condensation (and in particular intra- 

 atomic condensation) is in some way connected with physiological activity, as the 

 first is, and the second appears to be, diminished or removed by chemical addi- 

 tion. This suspicion is strengthened when we observe that in a very large pro- 

 portion of the cases as yet investigated saturated bodies (that is, bodies whose 

 condensation is 0) are inert, or nearly so. 



Kakodylic acid, as already mentioned, is a remarkable example of this, and 

 the salts of tetrethyl-arsonium % seem to be equally inert. Similarly, the salts of 

 tetramethyl-stibonium || are not emetic. So that, as far as experiment goes, it 

 would seem that the stable compounds of pentatomic arsenic and antimony have 

 a very different and much less strongly marked action than the compounds in 

 which these elements are contained as triads, or than those (such as arsenic acid) 



* Bunsen, Annalen der Chemie and Pharmacie, vol. xlvi. p. 10 (1843). 



f Stahlschmidt, Poggendorff 's Annalen, vol. cviii. p. 523 (1859). 



% Ibid. p. 541. 



§ Landolt, Annalen der Chemie und Pharmacie, vol. lxxxix. p. 331 (1854). 



|| Ibid. vol. Ixxxiv. p. 49 (1852). 



