INCREASE IN THE WEIGHT OF THE ENTIRE BODY. 47 



stances are implied, changes which are qualitative, as 

 contrasted with those evidently quantitative. After 

 the cells in the nervous system have developed in some 

 measure, they enter into relations with one another, 

 which are closer than those between the undeveloped 

 cells. The establishment of these relations constitutes 

 the organisation of the system a change by which 

 not only the strength, but also the complexity and 

 precision of its reactions are all increased. As a 

 matter of fact, both qualitative and quantitative modi- 

 fications go hand in hand, so that the distinction thus 

 made is merely formal. It will be possible to study 

 the growth of the central nervous system with a greater 

 advantage if the principal facts relating to the growth 

 of the entire body are first passed in review, and to 

 this task we now turn. 



The elements of the human body while growing are 

 continually undergoing chemical variations, which in 

 turn tend to cause variations in their specific gravity. It 

 is, therefore, to be remarked, that so far as the change 

 in the weight of man is concerned, variation in chemical 

 composition plays but an unimportant role. Taking 

 the body as a whole, the tissues of infants possess the 

 greater, those of the aged the smaller percentage of 

 water. For the foetus of one month Fehling 1 gives the 

 percentage of water as 97-5 per cent. At birth this 

 falls to 747 per cent. Bischoff found it to be 66'4 per 

 cent, at birth, whereas in an adult it was only 58*5 per 

 cent, of the weight of the body. The discrepancy between 

 these two determinations of water at birth is merely an 

 expression of the wide variations in this relation. When, 

 however, the separate organs of the new-born and aged 

 are compared in detail, it is by no means the case that 

 in each instance the percentage of water in the new- 

 1 Fehling, Arch. f. GyncekoL, 1877. 



