518 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



The various estimates of the maximal Duration of Life can only he 

 regarded, excepting in the case of the mouse, as very hazardous 

 approximations, since, even in the case of man, the maximal attainable 

 duration of life has been the subject of far more fables than investi- 

 gations. Probably the mean duration of life would be a better standard 

 of comparison than the maximal duration of life, since the magnitude 

 of the latter estimate may be so greatly affected by a single exceptional 

 observation. On the other hand statistical estimates of the average 

 duration of life are lacking, save for man and mice, and even the 

 estimates for man which are available include accidental deaths and 

 deaths from epidemic infections. However, notwithstanding the 

 approximate character of the estimates, they afford very striking evi- 

 dence of a tendency of Longevity to be associated with a high degree of 

 development of the nervous system. Thus, so far as the effect upon 

 the duration of life is concerned, exceptional development of the 

 nervous system exerts an effect similar to that which is induced by 

 the administration of an excess of a growth-catalyzer. 



The resemblance between the effects of a high proportion of Nervous 

 Tissues and those induced by administration of a growth-catalyzer 

 extends, however, even to the time-relations of growth, as expressed 

 by the contours of the growth-curve. Thus on comparing the growth- 

 curves for man and mice in Fig. 31 (p. 473), with the growth-curves for 

 cholesterol-fed and tethelin-fed mice in Figs. 40 and 41 (pp. 505 and 

 506), it is at once apparent that the change in the time relations of 

 the growth of mice which is induced by these catalyzers brings their 

 growth-curve into close approximation to the human curve. The effect 

 of the growth-catalyzers in unusual amount is to apparently prolong 

 the second and abbreviate and accelerate the third growth-cycle, and 

 it is in precisely these characteristics that the human growth-curve, 

 when reduced to the same scale, differs most strikingly from the 

 growth-curve for mice. It is not unlikely, therefore, that the differ- 

 ence in contour of the mouse and human curves of growth is attribu- 

 table to the greater abundance of endogenous catalyzers of growth in 

 the tissues and tissue-fluids of man consequent upon the greater pro- 

 portionate development of his nervous system. 



REFERENCES 



GENERAL CHARACTERISTICS OF THE GROWTH-PROCESS: 

 Voit, C.: Zeit. f. Biol., 1866, 2, p. 353. 

 Bowditch: Eighth Annual Report, State Board of Health, Massachusetts, U. S. A., 



1877. 



Roberts: Manual of Anthropometry, London, 1878. 



Anthropometric Committee, British Assn. Reports, 1879, p. 175; 1883, p. 253. 

 Minot: Jour. Physiol., 1891, 12, p. 97. 

 Porter: Trans. Acad. Sci., St. Louis, 1895, 6, p. 263. 

 Voit, E.: Zeit. f. Biol., 1905, 46, p. 195. 

 Donaldson: Boas Memorial Volume, New York, 1906, p. 5. The Rat, Pub. of the 



Wistar Institute, Philadelphia, 1915. 



Loeb, J.: Seventh Internat. Zool. Congress, Boston, 1907. 

 Ostwald: Vortrage und Aufsatze iiber Entwicklungsmech., Leipzig, 1908, Heft 5. 



