CHAPTER XX. 



PROCESSES INFERRED FROM INDIRECT OBSERVATION: 



GROWTH. 



GENERAL CHARACTERISTICS OF THE GROWTH-PROCESS. 



Regarded from the chemical point of view the growth of animals 

 consists, essentially, in the transformation of simple, unorganised 

 Foodstuffs, such as water, the inorganic salts, fats, carbohydrates, 

 amino-acids, and so forth into new chemical entities which, collectively 

 regarded, form the organised protoplasm of the animal tissues. 

 Growth, therefore, involves the synthesis of a variety of chemical 

 compounds in due proportion and succession to one another. 



This process obviously does not take place with uniform velocity 

 throughout life. It is not at all unusual, for example, for an infant to 

 grow, during the first months succeeding birth, at the rate of two 

 pounds per month. Were this rate of growth maintained, then at 

 twenty years of age we would weigh in the neighborhood of five 

 hundred pounds. 



Nevertheless the process of growth is not one which undergoes a 

 uniform retardation, diminishing in velocity by a uniform proportion 

 per annum. On the contrary, the growth of children, and of animals, 

 takes place in spurts, separated more or less distinctly from one 

 another by periods of relatively languid growth. Thus the rate of 

 growth in utero during the first half of gestation is so slow that prior 

 to this period the weight of the human foetus is inappreciable in com- 

 parison with that of the mother. This period of slow growth is suc- 

 ceeded by the extraordinarily rapid accretion of tissue which charac- 

 terises development duiing the months immediately prior to and 

 succeeding delivery. A definite slackening of growth occurs, however, 

 toward the end of the first year of extrauterine life, and this slowing 

 down of growth is not an artefact, dependent upon weaning, since it 

 occurs just as strikingly in bottle-fed infants. This resting period is 

 succeeded by the relatively rapid growth of the third, fourth, and fifth 

 years Another pause or slackening of growth succeeds this, to be 

 followed by the energetic growth which accompanies adolescence. 



The growth of man, therefore, consists of periods of rapid and slow 

 growth which alternate with one another, and if we plot the growth in 

 any dimension, for example the growth in weight, on " coordinate paper" 

 so that the weights are measured vertically and ages horizontally, we 

 obtain a diagrammatic picture of the growth-process which is not a 



