Chap, iv.] OF THE GENEEAL CONDITIONS OF GROWTH. 293 



is aged. The miiscular fibre of a yoimg animal contains 26 in 

 100 of water ; that of an adult of the same species only 23,5. 

 Haller, comparing the different degrees of cohesion of human 

 hair according to age, found that at eight years of age this 

 cohesion was represented by 10, at twenty-two by 17, and at 

 fifty-five by 25.i 



The degree of fluidity of the anatomical elements is great in 

 proportion to the youth of the animal, and the rapidity of reno 

 vation and of growth is correlative with it. According to the 

 tables of Quetelet, the growth of man is two-fifths the first year, 

 a seventh the second, an eleyenth the third, a fourteenth the 

 fourth, a fifteenth the fifth, and eighteenth the sixth and seventh. 

 .It is only a sixty-eighth at eighteen years, and a two hundredth 

 at nineteen. 



Upon the subject of the advantageous influence of suitable 

 humidification upon growth, Burdach points out that, in many 

 aquatic animals, fishes, amphibious, and cetaceous animals, growth 

 lasts as long as life, and is only gradually and more and more 

 retarded. 



The nutritive characteristic of youth is the rapidity and 

 facility of nutritive exchange. This is why the phenomena of 

 oolotu-ation and discolouration of the bones by madder are effected 

 with much greater rapidity when the animal is young. 



With the advance of age, all the secretions are impoverished, 

 especially the cutaneous perspiration ; at the same time the 

 general oxydation of the tissues lessens, the production of heat 

 diminishes ; all the functions become less energetic ; some are 

 extinguished by degrees, especially those of the most differen- 

 tiated histological elements, those most noble, least vegetative, 

 those of the nervous and muscular elements. Strength decreases, 

 and intelligence is blunted. 



This is because the ruling property of the living substance 

 gradually declines. Nutrition becomes less and less active, and 

 all the other properties of which it is the support decline with 

 1 Burdacli, Traiti de FTiysiologie, t. V. p. 491. 



