SENESCENCE IN HIGHER ANIMALS AND M A\ 



■/:> 



as age advances growth sooner or later gives place to reduction. 

 Data from the population of England' give essentially the same 

 results. Minot ('08) also gives data and curves from his own 

 investigations of the growth of guinea-pigs, rabbits, and chicks 

 which likewise show that the rate of growth decreases ver>' greatly, 



particularly during the early part of postem- 

 bryonic life. Figs. 1 1 1 and 1 1 2 are curves 

 from Minot's data showing the average daily 

 percentage increments in weight of male and 

 female rabbits beginning three days after birth. 

 The abscissae represent number of days after 

 birth; the ordinates, percentages. Here again 

 it is evident that the rate of growth decreases 

 with a few interruptions, at first very rapidly 

 and later more slowly. According to Donaldson 

 ('06) the curve of growth of the white rat is 

 very similar to that of man, except that the 

 length of the growth-period is much shorter. 

 If the decrease in the rate of growth is in any 



and 



Per cent 

 180 . 



160 .. 



140 .. 



120 .. 



100 .. 



80 



60 .. 



40 



20 



degree a measure of the rate of senescence- 



Years 



23456789 



Fig. 1 10 — Curve showing the decrease in the rate of growth in girls from the 

 first to the twenty-third year: similar to Fig. 109. From Miihlmann's tables (Miihl- 

 mann, '00), calculated from Quetelet's data. 



there can be little doubt that it is one of the features of senescence 

 — Minot is entirely correct in asserting that the rate of senescence 

 is highest in youth and lowest in advanced life. 



In most vertebrates, as well as in many invertebrates, the fmal 

 size of the individual is subject to relatively slight variation, and 

 the amount of growth during development is within certain limits 



' Figs. 38 and 39 and Tables II and III in Minot's Age, Growth and Death give 

 these statistics in graphic and tabular form as revised by Donaldson from Robert's 

 Manual of Anthropometry (1878). 



