THE FLUIDS OF THE BODY 47 



blood. The surplus of food is either stored or burnt. The 

 composition of lymph is unaffected. Its quality is not im- 

 proved by taking more food than enough. A perfect balance 

 is maintained. Every cell is able, when conditions are normal, 

 to obtain as much nutriment as it needs. It cannot get more. 

 It cannot lay by food and shirk work. If it did it would grow. 

 Reaching its optimum size, it would divide. Additional tissue 

 would be formed. But when it does more work it needs more 

 food ; and it is a matter of common experience that the system 

 is so adjusted that food is supplied to the tissues, not reluctantly, 

 but with a slight tendency towards generosity. Working 

 harder than usual, they find the lymph by which they are 

 bathed somewhat richer in the materials that they need than 

 the necessities of the case demand. They are able not merely 

 to obtain all they want, but a little more. Activity favours 

 growth. j^ 



Many attempts have been made to show that if a part of the 

 body has more than its share of food it grows to an excessive 

 size. John Hunter grafted a cock's spur into its comb. It 

 grew to monstrous dimensions. Such a result favours the 

 view, but it is not quite conclusive. Undoubtedly the comb was 

 richly supplied with blood, but it does not follow that the cells 

 of the spur were able in their new situation to take advantage 

 of this supply. Besides, the spur when projecting from the 

 head was not subject to the accidents to which it was exposed 

 whilst on the leg. Its size was not kept down by friction. Nor 

 was it as hard and compact as it would have been in its normal 

 situation. It is scarcely possible to devise any experiment that 

 would be satisfactory now that the relations between blood 

 and lymph and lymph and tissues are understood. In certain 

 pathological conditions, however, hypertrophy is the result of 

 the hypersemia of chronic inflammation ; and there is little 

 doubt that, if we could arrange for a certain group of cells to 

 receive lymph richer in food and freer from waste products 

 than the perfect adjustment of supply to needs normally allows, 

 the cells would grow. 



Under perfectly healthy normal conditions growth can be 

 induced only by use. Nature supplies the fuel which is used 

 during activity, and a balance of food available for the con- 

 struction of additional machinery. The muscle which is 



