86 



THE QUARTERLY REVIEW OF BIOLOGY 



The importance of these advances for the 

 general theory of biology does not seem 

 to have been sufficiently considered. 

 Driesch's expression "a harmonious equi- 

 potential system" undoubtedly seemed 

 impossible to imagine on a mechanical 

 basis at the time when he introduced the 

 term, but there is now not the same justi- 

 fication for pessimism. It is becoming 

 clearer and clearer that the living cell 

 exists in an extremely balanced condition, 

 well buffered, heavily poised, apt in every 

 way to resist influences tending to move 

 it out of its equilibrium position. Un- 

 successful attempts were made some years 

 ago by L. T. Troland (54) to relate the 

 phenomena of regulation in living cells 

 to the properties of enzymes, but though 

 these failed in detail he was nevertheless 

 on the right track. We may conclude 

 that it is possible, already and in spite 

 of the great incompleteness of our knowl- 

 edge of biophysics and biochemistry, to 

 point to purely physico-chemical systems 

 that would be bound to exhibit, when 

 working in intimate association, simple 

 forms of that tendency to constancy of 

 internal and external environment which 

 the neo-vitalists regarded as preeminently 

 the god in the machine. 



It is worth while also to study in this 

 connection the exact limits of regulation 

 power, for Lillie's question — "Why can 

 the salamander-entelechy regenerate a 

 leg but not the cat-entelechy?" has lost 

 none of its force. In embryology the re- 

 searches of Spemann and his school, 

 reviewed recently by Huxley (z6) and 

 de Beer (2.), have done much to clear 

 the air. The totipotence of the early 

 embryo, or rather, the approximation 

 towards the state of totipotence, which is 

 then observed, falls off rapidly as develop- 

 ment proceeds, and by the time of gastru- 

 lation the process of chemo-differentiation 

 sets in. After this, all development is 



irrevocably determined, ectoderm cells 

 will make ectoderm and nothing else, 

 until finally in the very late stages regu- 

 lation of form again becomes possible, 

 owing to the assumption of function; this 

 is the stage of Roux's "struggle of the 

 parts." "The inability of organisms to 

 regulate during the period of self- 

 differentiation of different organs can be 

 illustrated by the analogy of an army," 

 says de Beer, "whose staff at the outset 

 of the campaign has determined and as- 

 signed the duties of the various corps. 

 It loses control of these while they are 

 independently performing their allotted 

 tasks, and regains it again later when 

 inter-communication is reestablished. 

 The amazing results of regulation in 

 Clavellina, sea-urchin blastomeres, etc. 

 have led to the forms of vitalism which 

 have been developed by Driesch and 

 others. It is therefore interesting to find 

 that organisms do not always regulate." 



MINOR CONSIDERATIONS 



An interesting suggestion as to the 

 nature of tonus and trophic action in 

 living organisms has recently been made 

 by Sir W. B. Hardy (zz). The manner 

 in which nerve fibres control tonus and 

 heat-production in muscle, for instance, 

 has always been exceedingly obscure and 

 has furnished a theme for several neo- 

 vitalist physiologists. It is indeed true 

 that while we have considerable informa- 

 tion about the waves of nervous excitation 

 which produce muscular movement, we 

 know nothing at all about the nature of 

 trophic action and the control of tonus 

 in muscle. Hardy suggests that the 

 explanation may probably be found in 

 the orientation of molecules, a process 

 which can certainly happen in masses of 

 matter though it has been mostly studied 

 in surface films. Experiments with lu- 

 bricants demonstrate that layers of ori- 



