724 PHYSIOLOGY IN EEL AT ION TO 



The second great principle for the regulation of the understanding 

 of which I wish to speak, is one which, I believe, possesses less 

 currency and notoriety, and is less observed than it deserves. 

 This canon bids us, in considering a complex phaenomenon, to be 

 most careful that we omit none of the circumstances which can by 

 any possibility be of the essence of the case. And as the possi- 

 bilities of Nature are all but infinite — as, for example^ the investi- 

 gator of problems of Geographical Distribution knows well that a 

 'secret bond' may bind up together, and that inextricably, the 

 interests of organisms removed as far as possible to all appearance 

 from each other in the scale of life ; as a fly or a plant may, by its 

 increasing and multiplying, make half a continent uninhabitable or 

 inhabitable by the highest mammals ; I apprehend that in bio- 

 logical and medical problems, by the phrase ' all the circumstances 

 which can by any possibility be of the essence of the case,' we mean 

 practically, ' all the circumstances of the case,' without any quali- 

 fying limitation. But we will let Descartes, to whom the enuncia^ 

 tion of this rule is usually and, so far as I know, rightly assigned, 

 enunciate it for us in his own words. These run thus (CEuvres, 

 tom. xi. 1826, ed. V. Cousin, p. 23): ' R^gle Septieme pour la 

 Direction de I'Esprit. Pour completer la science, il faut que la 

 pensee parcoure d'un mouvement non interrompu et suivi tous les 

 objets qui appartiennent au but qu'elle veut atteindre et qu'ensuite 

 elle les resume dans une enumeration m^thodique et suffisante.' 

 Some of the very greatest advances which have been made of late 

 in practical diagnosis have been made in the spirit of this recom- 

 mendation. The application of a chemical test to the urine for 

 information as to the expediency of giving or withholding wine in 

 the case of a sinking life, would have seemed to Swift, could he 

 have had any idea either of such a procedure or of the employment 

 of a sphygmograph for the same object, more absurd than any 

 of the follies he ascribed to the philosophers of Laputa. But as 

 Archbishop Whately — a name to be greatly honoured here, and, 

 indeed, wherever else liberality, and fearlessness, and ability are 

 held in respect — has well pointed out, the absurdities of Laputan 

 aspirations are less wonderful than the actual attainments of 

 modern science. And to these results science has attained, because 

 her votaries have known that what may seem to Swift, and such as 

 Swift, to be but curious and dilettante, otiose, or even disgusting, 



