vii THE STAGES OF LIFE AND DEATH 279 



between the new-born baby and the child who is nearing puberty, 

 we are driven to the conclusion that no other period of extra- 

 uterine life shows such a far-reaching functional transformation 

 and such a rapid development of the body as the brief period of 

 infancy. The period of growth par excellence is infancy, and if 

 we would determine the characteristics of infantile life, we must 

 have some notion of the theory of growth. 



In every species, race, and family growth takes place in 

 accordance with certain laws of evolution resulting from biological 

 forces which are transmitted with the hereditary patrimony. 

 Certain external conditions, such as nourishment and mode of life, 

 may modify growth within certain narrow limits, but the influence 

 of these factors is a negligible quantity compared to that of 

 heredity. When treating of the problem of the transmission of 

 the characteristics of parents to their offspring, we saw in 

 Chapter V. that science is unable to account for it and can only 

 hazard certain vague and bold hypotheses by way of explanation. 

 We are ignorant of the physical conditions which bring about the 

 multiplication and cellular differentiation of the germ resulting 

 from the fusion of the two sexual elements until in course of time 

 it assumes a typical form and becomes a determined organic mass 

 which is almost constant in the individual species and varieties. 

 Here we have the baffling problem formulated by Aristotle in 

 the following words : " causae explicandae sunt, quamobrem 

 auimalium alia longum aetatis tempus conficiant, alia breve." 



We have learnt but little of the primum movens of cellular 

 multiplication since Haller's day; Loeb by the use of chemicals 

 (hydro -chlorate of manganese) succeeded in exciting the first 

 phases of development in eggs of echinoderms and annelides. 

 He regarded the nucleus of the cell as a ferment for its own 

 synthesis of nuclein, and believes that the autokatalytic character 

 of this synthesis is the basis of the hereditary continuity of life. 

 Ostwald and Robertson have endeavoured to prove that the curves 

 of growth, i.e. of the gradual increase in weight and cellular 

 multiplication of organisms, assume the aspect peculiar to auto- 

 katalytic reactions. These ingenious hypotheses fail however 

 to explain why the fertilised ovum should in the course of its 

 development tend to reproduce in the offspring the specific form 

 of the parents, their features and sometimes even certain of their 

 peculiarities. 



On the other hand, Max Rubner has enabled us to lay down 

 certain laws to which growth in relation to the exchange of 

 material and energy is subject once it has been begun by fertilisa- 

 tion. It is governed by two fundamental facts : 



(a) No animal cell can grow and multiply without developing 

 heat. Eubner calculated for the foetal life of mammals the 

 number of calories which can be developed during the formation 



