CHAP. HI.] THE PHASES OF LIFE. 1145 



in weight twelve times only between liirtli and full growth, 

 whereas the whole body increases twenty times. The heart 

 and the liver according to the newer observations behave very 

 similarly, and even according to the older observations lag con- 

 siderably behind the whole frame, whereas the lungs and the 

 alimentary canal almost exactly keep pace with it, and the 

 skeletal framework, in spite of its being specifically lighter in 

 its earlier cartilaginous condition, maintains throughout life 

 very nearly the same relative weight. The muscles on the 

 contrary grow more than twice as fast as the whole body ; t he- 

 great increase in these covers the relative decrease of the other 

 parts, and it is largely by the laying on of flesh and fat that 

 the bal>e gains the bulk of the man. 



713. We usually measure growth by taking account of 

 two sets of changes, changes of stature and changes of weight ; 

 and we may study both these changes in more than one way. 



If we measure the height at intervals we may plot out the 

 curve of growth of stature , and when we do this we find that 

 the curve rises rapidly at first but afterwards more slowly, 

 shewing that the increment is decreasing, and at about the 

 twenty-fifth year ceases to rise at all. From thence to about 

 fifty years of age the height remains stationary, after which 

 there may be a decrease, especially in extreme old age. The 

 curve moreover is not regular, but indicates by its changes 

 that the increment of height in a given time is now smaller, 

 now greater. 



The curve of weight is, on the whole, at first very similar 

 to that of height, rising in a somewhat similar way and shew- 

 ing similar irregularities^ but instead of ceasing to rise at 

 about the twenty-fifth year it continues to rise, though marked 

 with many irregularities, and may continue to do so until about 

 the fortieth year. After the sixtieth year a decline of variable 

 extent is generally witnessed. It should be noted that in the 

 first few days of life, so far from there being an increase, there 

 is an actual decrease of weight, so that, even on the seventh 

 day the weight still continues to be less than at birth ; and a 

 similar post-natal loss of weight is observed in animals. I f we 

 take the curve of growth from the impregnation of the ovum 

 onwards this post-natal loss of weight will appear as an abrupt 

 change in the curve due to the so to speak violent act of birth. 

 It should be added that the curves both of height and weight 

 exhibit differences dependent on sex, circumstances, race, cli- 

 mate and the like. 



We may also study the progress of growth by measuring 

 the increment of growth in a given time, in a year for instance, 

 and plotting out the curve of the yearly increment. When we 

 do this we obtain very instructive results. We find that tin- 

 yearly increment decreases very rapidly during the first two 



