280 PHYSIOLOGY CHAP. 



of a given mass of living substance, and arrived at the following 

 results : the horse, 2028 ; the pig, 2210 ; the sheep, 2728 ; and the 

 dog, 3318. In the case of man the figures must be higher owing 

 to his longer period of development. 



(6) Consumption and destruction of substance always coincide 

 with the phenomenon of growth. The researches of Parrot and 

 Robin (1876) prove that a new-born infant for a given weight 

 absorbs more oxygen and twice as much nitrogen as the same 

 weight of an adult and discharges only a sixth of the amount of 

 urea, because a large portion of the nitrogen is retained for the 

 requirements of growth. On the other hand, dissimilation is very 

 active in the new-born, and the kidneys in proportion to the 

 weight of the body are twice as large as those of the adult. 



Rubner gave the name quotient of growth to the percentage 

 relationship between the sum of accumulated energy, deduced 

 from the increase in weight, and the- sum of energy consumed in 

 the process of dissimilation. This quotient is very high after 

 birth ; it decreases until it reaches zero in the higher animals, 

 whereas in unicellular creatures it appears to be an invariable 

 constant. 



The determination of this quotient in the animal scale brings 

 out an unexpected fact, namely, that the consumption of energy 

 in the processes of disintegration, which are more intense in the 

 growing than in the resting cell, is much greater than the energy 

 expended on growth. 



Rubner states that the different organisms use different 

 quantities of nutritive material for the increase of their body weight. 

 The Schizomycetes, which can double their size in a few minutes, 

 accumulate during growth 12-31 per cent of the total energy 

 introduced. The definite size of an animal is, however, not only 

 dependent upon the length of the period of growth, but is also 

 bound up with specific and individual properties. 



If with Rubner we consider the time taken by the new-born 

 animal to double its weight, we find the rabbit takes 6 days, the 

 dog and cat 9, the pig and sheep 14-15, the ox 47, the horse 60, 

 and man 180. If, therefore, man as compared with the rabbit 

 takes thirty times as long to double his own weight, he must 

 consume a correspondingly greater amount of nourishment in 

 order to acquire a similar weight of body substance. 



If we calculate the energy consumed in the time during which 

 a kilogramme of new-born animal doubles its own weight and 

 express the result in calories, we arrive at the following figures : 

 horse, 4512 ; ox, 4243 ; sheep and pig, about 3800 ; dog, 4304 ; 

 rabbit, 5066 ; man, 28,864. Thus the total amount of energy 

 expended in doubling the weight of the animal is much the same 

 irrespective of the length of the period of growth, except in the 

 case of man, whose consumption of energy is much greater. 



