12 INTRODUCTORY [ch. 



inanimate bodies*." And Theodore Schwann said plainly, a hun- 

 dred years ago, "Ich wiederhole iibrigens dass, wenn hier von einer 

 physikahschen Erklarung der organischen Erscheinungen die Rede 

 ist, darunter nicht nothwendig eine Erklarung durch die bekannten 

 physikalischen Krafte. . .zu verstehen ist, sondern iiberhaupt eine 

 Erklarung durch Krafte, die nach strengen Gesetzen der blinden 

 Nothwendigkeit wie die physikalischen Krafte wirken, mogen diese 

 Krafte auch in der anorganischen Natur auftreten oder nicht f." 



Helmholtz, in a famous and influential lecture, and surely with 

 these very words of Schwann's in mind, laid it down as the funda- 

 mental principle of physiology that "there may be other agents 

 acting in the hving body than those agents which act in the inorganic 

 world ; but these forces, so far as they cause chemical and mechanical 

 influence in the body, must be quite of the same character as inorganic 

 forces : in this, at least, that their eff'ects must be ruled by necessity, 

 and must always be the same when acting under the same conditions ; 

 and so there cannot exist any arbitrary choice in the direction of their 

 actions." It follows further that, like the other "physical" forces, 

 they must be subject to mathematical analysis and deduction J. 



So much for the physico-chemical problems of physiology. Apart 

 from these, the road of physico-mathematical or dynamical investi- 

 gation in morphology has found few to follow it; but the pathway 

 is old. The way of the old Ionian physicians, of Anaxagoras § , of 

 Empedocles and his disciples in the days before Aristotle, lay just 

 by that highway side. It was Galileo's and Borelli's way; and 

 Harvey's way, when he discovered the circulation of the blood ||. 

 It was little trodden for long afterwards, but once in a while 

 Swammerdam and Reaumur passed thereby. And of later years 

 Moseley and Meyer, Berthold, Errera and Roux have been among 



* Croonian Lecture on the heart and arteries, Phil. Trans. 1809, p. 1; Collected 

 Works, I, p. 511. 



t M ikroskopische Untersuchungen, 1839, p. 226. 



J The conservation of forces applied to organic nature, Proc. Royal Inst. 

 April 12, 1861. 



§ Whereby he incurred the reproach of Socrates, in the Phaedo. See Clerk 

 Maxwell on Anaxagoras as a Physicist, in Phil. Mag. (4), xlvi, pp. 453-460, 1873. 



II Cf. Harvey's preface to his Exercitationes de Generatione Animalium, 1651: 

 "Quoniam igitur in Generatione animalium (ut etiam in caeteris rebus omnibus 

 de quibus aliquid scire cupimus), inquisitio omnis a caussis petenda est, praesertim 

 a materiali et efficiente: visum est mihi" etc. 



