184 THE RATE OF GROWTH [ch. 



or dog, it passes through the same phases of growth ; and, to quote 

 Dr Johnson again, "whatsoever is formed for long duration arrives 

 slowly to its maturity*." In all cases growth begins slowly; it 

 attains a maximum velocity somewhat early in its course, and 

 afterwards slows down (subject to temporary accelerations) towards 

 a point where growth ceases altogether. But in cold-blooded 

 animals, as fish or tortoises, the slowing down is greatly protracted, 

 and the size of the creature would seem never to reach, but only 

 to approach asymptotically, to a maximal limit. This, after all, 

 is an important difference. Among certain still lower animals 

 growth ceases early but Hfe goes on, and draws (apparently) to no 

 predetermined end. So sea-anemones have been kept in captivity 

 for sixty or even eighty years, have fed, flourished and borne 

 offspring all the while, but have shewn no growth at all. 



The rate of growth of various parts or organs f 



That the several parts and organs of the body, within and 

 without, have their own rates of growth can be amply demonstrated 

 in the case of man, and illustrated also, but chiefly in regard to 

 external form, in other animals. There lies herein an endless 

 field for the study of correlation and of variability J. 



In the accompanying table I show, from some of Vierordt's data, 

 the relative weights at various ages, compared with the weight at 

 birth, of the entire body, and of brain, heart and liver; also the 

 changing relation which each of these organs consequently bears, 

 as time goes on, to the weight of the whole body (Fig. 47) §. 



* All of which is tantamount to a mere change of scale of the time-curve. 



f This phenomenon, of incrementum inequale, as opposed to incrementum in 

 universum, was most carefully studied by Haller: "Incrementum inequale multis 

 modis fit, ut aliae partes corporis aliis celerius increscant. Diximus hepar minus 

 fieri, majorem pulmonem, minimum thymum, etc." (Elem. viii (2), p. 34.) 



X See {int. al.) A. Fischel, Variabilitat und Wachsthum des embryonalen 

 Korpers, Morphol. Jahrb. xxiv, pp. 369-404, 1896; Oppel, Vergleickung des 

 Entwickelungsgrades der Organe zu verschiedenen Entwickelungszeiten hei Wirhel- 

 thieren, Jena, 1891; C. M. Jackson, Pre-natal growth of the human body and the 

 relative growth of the various organs and parts, Amer. Journ. of Anat. ix, 1909; 

 and of the albino rat, ibid, xv, 1913; L. A. Calkins, Growth of the human body in 

 the foetal period. Rep. Amer. Assoc. Anat. 1921. For still more detailed measure- 

 ments, see A. Arnold, Korperuntersuchungen an 1656 Leipziger Studenten, Ztschr. 

 f. Konstitutionslehre, xv, pp. 43-113, 1929. 



§ From Vierordt's Anatomische Tabellen, pp. 38, 39, much abbreviated. 



