AN INTRODUCTION To THE STUDY OF GROWTH. 35 



practically amounts to nothing, and then it is that the 

 body becomes most susceptible to destructive influences 

 continuously at work upon it. With the decay of any 

 portion of the organism comes a disturbance of the 

 balance in the work allotted to the several portions. 

 The other tissues not specialised for the purpose are 

 forced to take on the functions of those already 

 damaged, and this they can do but imperfectly. The 

 result is progressive enfceblement of these overtaxed 

 cells, until finally some function is so imperfectly per- 

 formed that the life processes are blocked, and the 

 organism as a whole dies. Minot pointed out that in 

 the mature cell the proportion of cytoplasm to nucleus 

 was greater than in the growing animal ; and on the 

 ground of this propounds, half humorously, the 

 aphorism, that " Protoplasm is the physical basis of 

 advancing decrepitude." By thus granting that the. 

 cytoplasm is in some way a hindrance to its own 

 activity, the specialised body-cells are seen to be similar 

 to the unicellular organisms, among which cell-enlarge- 

 ment is so clearly self-limited. But it is plain that in 

 speaking of cells and the relative development of their 

 different portions, we are using these variations in the size 

 of the nucleus and the cytoplasm merely as indices of 

 more subtle structural and chemical changes which will 

 form the proper basis for a future explanation. 



Though we infer that the ability to grow is, so far as 

 it goes, a protection against commencing deterioration, 

 yet a search for illuminating details does not yield much 

 because of our meagre information concerning the length 

 of life in animals. Popularly birds, reptiles, batrachians, 

 and fishes are considered capable of living for very many 

 years. It further appears that some reptiles and some 

 fishes continue to grow almost as long as they live, but 

 in later life their growth is certainly very slow. At the 



