CHAP, in.] THE PHASES OF LIFE. 407 



growing frame is the prominence of the lymphatic system. Not 

 only are the lymphatic glands largely developed and more active 

 (as is probably shewn by their tendency to disease in youth), but 

 the quantity of lymph circulation is greater than in later years. 

 Characteristic of youth is the size of the thymus body, which 

 increases up to the second year, and may then remain for a while 

 stationary, but generally before puberty has suffered a retro- 

 gressive metamorphosis, so that very often hardly a vestige of it 

 remains behind. The thyroid body is also relatively greater 

 in the babe than in the adult ; the spleen, on the other hand, 

 relatively to the body-weight does not change greatly, though 

 rather smaller in the adult. As we have already said the recupera- 

 tive power of infancy and early youth is very marked. 



The quantity of urine passed, though scanty in the first two 

 days, rises rapidly at the end of the first week, and in youth the 

 quantity of urine passed is, relatively to the body-weight, larger 

 than in adult life. This may be, at least in quite early life, partly 

 due to the more liquid nature of the food, but is also in part the 

 result of the more active metabolism. For riot only is the quantity 

 of urine passed, but also the amount of urea and of some other 

 urinary constituents excreted, relatively to the body-weight, 

 greater in the child than in the adult. The presence of uric acid, of 

 oxalic acid, and according to some, of hippuric acid in unusual 

 quantities is a frequent characteristic of the urine of children. It 

 is stated that calcic phosphates, and indeed the phosphates gen- 

 erally, are deficient, being retained in the body for the building up 

 of the osseous skeleton. 



975. It would be beyond the scope of this work to enter 

 into the psychical condition of the babe or the child, and our 

 knowledge of the details of the working of the nervous system in 

 infancy is too meagre to permit of any profitable discussion. It is 

 hardly of use to say that in the young the whole nervous system 

 is more irritable or more excitable than it is in later years ; by 

 which we probably to a great extent mean that it is less rigid, 

 less marked out into what, in preceding portions of this work, 

 we have spoken of as nervous mechanisms. In new-born puppies 

 and some other animals stimulation of the various cerebral areas 

 does not give rise to the usual localized movements ; these do not 

 appear until some time after birth ; but in this respect differences 

 are observed in different kinds of animals corresponding to the well 

 known differences between different kinds of animals in the powers 

 possessed at birth ; the human babe as regards the latter is inter- 

 mediate between the puppy and the young guinea-pig. As we have 

 seen, the fibres of the various tracts in the central nervous system 

 acquire their medulla at different epochs; there is experimental 

 evidence in support of the view, otherwise probable, that the as- 

 sumption of functional activity follows in the same order ; and the 

 pyramidal tract is as we have seen the one in which the fibres are 



