THE CONDITION OF OLD AGE 31 



we come to study these various animals more care- 

 fully, we learn that in them the anatomical and phy- 

 siological features which I have indicated to you in 

 my description of the changes in the human being 

 are paralleled, as it were, by similar changes ; but 

 only by similar, not by identical, changes. If we 

 examine the insects, for instance, we see that in an 

 old insect there is a hardening of the outer crust of 

 the body which serves as a shell and a skeleton at 

 once. That hardening increases with the age of the 

 individual. We can see in the insect a lessening 

 development of the digestive tract, and we can see 

 it has been demonstrated with particular nicety a 

 degradation of the brain. 1 Insects have a very small 

 brain, but when a bumblebee, or a honeybee, grows 

 old, as he does in a few weeks after he acquires 

 his wings, we see that the brain actually becomes 

 smaller, and not only that, but as I shall be able 

 to demonstrate to you with the lantern in the 

 next lecture, the elements which build up the brain 

 have each of them become smaller and the diminu- 

 tion in the size of the brain is due in part to the 

 shrinkage of the single microscopic constituents. 

 There is another point of resemblance. We find 

 that when one of the better parts of the body under- 

 goes an atrophy, it becomes not only smaller, but its 

 place is to a certain extent taken by the inferior 



1 C. F. Hodge, "Changes in Ganglion-Cells from Birth to Senile Death. 

 Observations on Man and Honeybee," Journal of Physiology, vol. xvii., pp. 

 129-134 (1894). 



