INTERMIXTURE OF EFFECTS. 



29S 



body, »nd, by reasoning from these, 

 would attempt to discover whether 

 mercury will act upon the body when 

 in the morbid condition supposed, in 

 Buch A manner as would tend to 

 restore health. The experimental 

 method would simply administer mer- 

 cury in as many cases as possible, 

 noting the age, sex, temperament, 

 and other peculiarities of bodily con- 

 stitution, the particulf^r form or variety 

 of the disease, the particular stage of 

 its progress, &c., remarking in which 

 of taese cases it was attended with a 

 •ialutary effect, and with what cir- 

 cumftances it was on those occasions 

 combined. The method of simple 

 observation would compare instances 

 of recovery, to find whether they 

 agreed in having been preceded by 

 the administration of mercury ; or 

 would compare instances of recovery 

 with instances of failure, to find cases 

 which, agreeing in all other respects, 

 differed only in the fact that mercury 

 had been administered or that it had 

 not. 



§ 7. That the last of these three 

 modes of investigation is applicable 

 to the case, no one has ever seriously 

 contended. No conclusions of value 

 on a subject of such intricacy ever 

 were obtained in that way. The 

 utmost that could result would be a 

 vague general impression for or against 

 the efficacy of mercury, of no avail 

 for guidance unless confirmed by one 

 of the other two methods. Not that 

 the results which this method strives 

 to obtain would not be of the utmost 

 possible value if they could be obtained. 

 If all the cases of recovery which pre- 

 sented themselves, in an examination 

 extending to a. great number of in- 

 stances, were cases in which mercury 

 had been administered, we might 

 generalise with confidence from this 

 experience, and should have obtained 

 a conclusion of real value. But no 

 such basis for generalisation can we, 

 in a case of this description, hope to 

 obtain. The reason is that which 

 we have spoken of as constituting 



the characteristic imperfection of the 

 Method of Agreement — Plurality of 

 Causes. Supposing even that mercury 

 does tend to cure the disease, so many 

 other causes, both natural and arti- 

 ficial, also tend to cure it, that there 

 are sure to be abundant instances ef 

 recovery in which mercury has not 

 been administered : unless, indeed, 

 the practice be to administer it in 

 all cases ; on which supposition it 

 will equally be found in the cases of 

 failure. 



When an effect results from the 

 union of many causes, the share which 

 each has in the determination of the 

 effect cannot in general be great ; and 

 the effect is not likely, even in its 

 presence or absence, still less in its 

 variations, to follow, even approxi- 

 mately, any one of the causes. Re- 

 covery from a disease is an event to 

 which, in every case, many influences 

 must concur. Mercury may be one 

 such influence ; but from the very 

 fact that there are many other such, 

 it will necessarily happen that al- 

 though mercury is administered, the 

 patient, for want of other concurring 

 influences, will often not recover, and 

 that he often will recover when it is 

 not administered, the other favourable 

 influences being sufficiently powerful 

 without it. Neither, therefore, will 

 the instances of recovery agree in the 

 administration of mercury, nor will 

 the instances of failure agree in its 

 non-administration. It is much if, 

 by multiplied and accurate returns 

 from hospitals and the Hke, we can 

 collect that there are rather more 

 recoveries and rather fewer failures 

 when mercury is administered than 

 when it is not ; a result of very 

 secondary value even as a guide to 

 practice, and almost worthless as » 

 contribution to the theory of the sub- 

 ject.* 



* It is justly remarked by Professor Bain, 

 that though the Methods of Agreement and 

 Difference aie not applicable to these cases, 

 they are not wholly inaccessible to the 

 Method of Concomitant Variations. " If 

 a cause happens to vary alone, the effect 

 will also vary alone : a cause and effect 



