MULTIPLICATION OF THE HUMAN RACE. 517 



vidual and adds to the production of new individuals: the 

 difference between the cases being, that instead of a better 

 external supply of materials there is a better internal 

 utilization of materials. Creatures of the same species noto- 

 riously differ in goodness of constitution. Here there is some 

 visceral defect, showing itself in feebleness of all the func- 

 tions; while here some peculiarity of organic balance, some 

 high quality of tissue, some abundance or potency of the 

 digestive juices, gives to the system a perpetual high tide of 

 rich blood, which serves at once to enhance the vital activities 

 and to raise the power of propagation. Such variations, 

 however, are independent of changes in the proportion be- 

 tween Individuation and Genesis. This remains the same, 

 while both are increased or decreased by the increase or 

 decrease of the common stock of materials. 



An illustration will best clear up any perplexity. Let us 

 say that the fuel burnt in the furnace of a locomotive steam- 

 engine, answers to the food which a man consumes. Let us 

 say that the produced steam expended in working the engine, 

 corresponds to that portion of absorbed nutriment which 

 carries on the man's functions and activities. And let us 

 say that the steam blowing off at the safety-valve, 

 answers to that portion of the absorbed nutriment which 

 goes to the propagation of the race. Such being the condi- 

 tions of the case, several kinds of variations are possible. 

 All other circumstances remaining the same, there may be 

 changes of proportion between the steam used for working 

 the engine and the steam that escapes by the safety-valve. 

 There may be a structural or organic change of proportion. 

 By enlarging the safety-valve or weakening its spring, while 

 the cylinders are reduced in size, there may be established a 

 constitutionally-small power of locomotion and a constitu- 

 tionally-large amount of escape-steam ; and inverse variations 

 so produced, will answer to the inverse variations between 

 Individuation and Genesis which different types of organisms 



