1896.] on Ludwig and Modern Physiology. 25 



eliminated. It is one and the same method throughout, by which, 

 step by step, knowledge perfects itself — at one time by discovering 

 errors, at another by correcting them ; and if at certain stages in this 

 progress difficulties seem insuperable, we can gain nothing by calling 

 in, even provisionally, the aid of any sort of Eidolon, whether " cell," 

 " protoplasm," or internal principle. 



It thus appears to be doubtful whether any of the biological 

 writers wLo have recently professed vitalistic tendencies are in reality 

 vitalists. The only exception that I know is to be found in the 

 writings of a well-known worker, Hans Driesch,* who has been led by 

 his researches on what is now called the Mechanics of Evolution, to 

 revert to the fundamental conception of vitalism, that the laws which 

 govern vital processes are not physical, but biological— that is, pecu- 

 liar to the living organism, and limited thereto in their operation. 

 Driesch's researches as to the modifications which can be produced by 

 mechanical interference in the early stages of the process of onto- 

 genesis have enforced upon him considerations which he evidently 

 regards as new, though they are familiar enough to Physiologists. 

 He recognises that although by the observation of the successive 

 stages in the ontogenetic process, one may arrive at a perfect know- 

 ledge of the relation of these stages to each other, this leaves the 

 efficient causes of the development unexplained (fiiJirt nicht zu einem 

 Erhenntniss ilirer hewirkenden Ursachen) — it does not teach us why one 

 form springs out of another. This brings him at once face to face 

 with a momentous question. He has to encounter three possibilities — 

 he may either join the camp of the biological agnostics and say with 

 du Bois-Eeymond, not only " ignoramus " but " ignorahimits " ; or be 

 content to work on in the hope that the physical laws that underlie 

 and explain organic Evolution may sooner or later be discovered ; or 

 he may seek for some hitherto hidden Law of Organism, of which the 

 known facts of Ontogenesis are the expression, and which, if accepted 

 as a Law of Nature, would explain everything. Of the three alterna- 

 tives Driesch prefers the last, which is equivalent to declaring himself 

 an out-and-out vitalist. He trusts by means of his experimental 

 investigations of the Mechanics of Evolution to arrive at " elementary 

 conceptions " on which by " mathematical deduction " | a complete 

 theory of Evolution may be founded. 



If this anticipation could be realised, if we could mentally 

 construct with the aid of these new Principia the ontogeny of a single 

 living being, the question whether such a result was or was not incon- 



* Driesch, ' Entwicklungsmeclianische Studieu ' : a Series of ten Papers, of 

 whicli the first six have appeared in the ' Zeitsch. f. w. Zoologie,' vols. liii. and 

 Iv. the rest in the ' Mittheilungen ' of the Naples Station. 



t " Elementarvorstellungen .... die zwar mathematische Deduktion aller 

 Erscheinungen aus sich gestatten mdchten." Driesch, " Beitrage ziir theore- 

 tischen Morphologic." ' Biol. Centralblatt,' vol. xii. p. 539, 1892. 



