Ill] GROWTH AND CATALYTIC ACTION 133 



which tends to double its numbers every few minutes, till (were 

 it not for limiting factors) its numbers would be all but incalculable 

 in a day*, is a simple but most striking illustration of the potenti- 

 alities of protoplasmic catalysis ; and (apart from the large share 

 taken by mere "turgescence"' or imbibition of water) the same 

 is true of the growth, or cell-multiplication, of a multicellular 

 organism in its first stage of rapid acceleration. 



It is not necessary for us to pursue this subject much further, 

 for it is sufficiently clear that the normal "curve of growth" of 

 an organism, in all its general features, very closely resembles the 

 velocity-curve of chemical autocatalysis. We see in it the first 

 and most typical phase of greater and greater acceleration ; this 

 is followed by a phase in which limiting conditions (whose details 

 are practically unknown) lead to a falling off of the former 

 acceleration ; and in most cases we come at length to a third phase, 

 in which retardation of growth is succeeded by actual diminution 

 of mass. Here we may recognise the influence of processes, or 

 of products, which have become actually deleterious ; their 

 deleterious influence is staved off for awhile, as the organism draws 

 on its accumulated reserves, but they lead ere long to the stoppage 

 of all activity, and to the physical phenomenon of death. But 

 when we have once admitted that the limiting conditions of 

 growth, which cause a phase of retardation to follow a phase 

 of acceleration, are very imperfectly known, it is plain that, 

 ipso facto, we must admit that a resemblance rather than an 

 identity between this phenomenon and that of chemical auto- 

 catalysis is all that we can safely assert meanwhile. Indeed, as 

 Enriques has shewn, points of contrast between the two phenomena 

 are not lacking ; for instance, as the chemical reaction draws to 

 a close, it is by the gradual attainment of chemical equilibrium: 

 but when organic growth draws to a close, it is by reason of a very 

 different kind of equilibrium, due in the main to the gradual 

 differentiation of the organism into parts, among whose peculiar 



* B. coli-comynunis, according to Buchner, tends to double in 22 minutes; in 

 24 hours, therefore, a single individual would be multiplied by something like 

 10-8; Sitzung.<<ber. Munchen. Ges. MorphoJ. u. Physiol, in, pp. 65-71, 1888. Cf. 

 Marshall Ward, Biology of Bacillus ramosus, etc. Pr. R. S. lviii, 265-468, 1895. 

 The comparatively large infusorian Stylonichia, according to Maupas, would 

 multiply in a month by 10*^. 



