VII 



THE STAGES OF LIFE AND DEATH 



281 



In the determination of the amount of energy contained in the 

 food used for the purpose of growth, Kubner found that whereas 

 the above-mentioned animals absorb during the first period of 

 doubling their own weight on an average 34-30 per cent of the 

 calories introduced, man stores up only 5-2 per cent, i.e. hardly 

 more than a seventh. 



Man further differs from other animals in the length of his 

 intra - uterine development, which in other animals usually 

 increases with the rise in the body weight. Thus the young of 

 man and the sheep weigh the same at birth, but the foetal life 

 of the sheep is only half as long as that of man and the difference 

 in their development during extra -uterine life is still more 

 marked. 



The extent and different kind of growth of animals are 

 determined after fertilisation, for the exchange of material in the 

 ovum does not differ much from that of the cells of the maternal 

 organism, whose consumption of energy varies especially in 

 proportion to the total size. After fertilisation the ovum shows 

 an exchange of material varying according to its origin and the 

 period of development of the organism arising from it will also 

 differ. With fertilisation all cells acquire the maximum quotient 

 of growth, but after birth the energy of growth gradually 

 diminishes each time the mass of the body is doubled until it 

 reaches zero and the animal attains its full size. 



Bodily growth is undoubtedly brought about by the exchange 

 of material and energy in the new-born animal ; an animal in 

 which metabolism takes place more rapidly will double its weight 

 in a shorter time and build up in that space of time the same 

 amount of substance as an animal, in which metabolism takes 

 place more slowly, would in a longer period. 



From the facts which we have enumerated it is obvious that 

 man occupies a unique position as compared with other mammals ; 

 his increase in size during his intra-uterine life and the whole of 

 the anaplastic stage is small in proportion to the intensity of his 

 exchange of energy. Eubner notes another interesting point : that 

 man differs from other mammals in the total amount of energy 

 used in a state of rest after the expiration of the anaplastic period. 



