36 EX VIRIBUS VIVIMUS. 



add, for carrying on the work of life. This same 

 store of living matter is called upon and reduced 

 in cases of great expenditure of force, such as are 

 greater than the contemporaneous power of assimi- 

 lation can supply ; and it seems not impossible that 

 this germinal matter may be the store from which 

 Professor Parkes supposed a muscle to draw a supply 

 of nitrogenous aliment in the absence of nitrogenous 

 food, and when only carbo-hydrates and hydro-car- 

 bons had been supplied. This is consistent with what 

 is known of the great danger of excessive exertion, 

 especially in the absence of abundant nutriment. 



The ovum is cornposed, in its very earliest stages, 

 of nothing but this protoplasm.^ As development 

 and growth advance, it gives rise to the formed tissues, 

 increasing itself also in bulk. But the germinal 

 matter never increases at the same rate as the whole 

 organism ; it is always diminishing relatively to the 

 whole, though increasing absolutely as long as growth 

 continues. This gives us some insight into the way 

 in which the change in the vitality of youth and age 

 occurs. 



But there is a more important action than this. 

 What is it that limits growth .' what gives the limit 

 to size ? Mr. Herbert Spencer (' Principles of Biology,' 

 vol. i. p. 128) very fully enters into this matter, and 

 clearly shews that expenditure (expenditure which uses 



' There is not even a cell-wall, according to the recent very important 

 researches of Dr. Edouard Van Beneden. 



