78 



THE NERVOUS SYSTEM 



every hospital in the civilised world, not only for 

 the saving of life, but also for the diagnosis and 

 medical or surgical treatment of innumerable 

 varieties of disease or injury of the brain, the 

 cord, or the nerves. Sir Michael Foster, in a 

 short summary of the problems of physiology, 

 puts clearly these consummate difficulties of the 

 physiology of the nervous system : — 



" In the first place there are what may be called 

 general problems, such as, How the food, after its 

 preparation and elaboration into blood, is built up 

 into the living substance of the several tissues ? 

 How the living substance breaks down into the 

 dead waste? How the building up and breaking 

 down differ in the different tissues in such a way 

 that energy is set free in different modes, the 

 muscular tissue contracting, the nervous tissue 

 thrilling with a nervous impulse, the secreting 

 tissue doing chemical work, and the like ? To 

 these general questions the answers which we can 

 at present give can hardly be called answers at 

 all. 



In the second place there are what may be called 

 special problems, such as, What are the various 

 steps by which the blood is kept replenished with 

 food and oxygen, and kept free from an accumula- 

 tion of water, and how is the activity of the 

 digestive, respiratory, and excretory organs, which 

 effect this, regulated and adapted to the stress of 

 circumstances ? What are the details of the vascu- 

 lar mechanism by which each and every tissue is 

 for ever bathed with fresh blood, and how is that 

 working delicately adapted to all the varied changes 

 of the body ? And, compared with which ail other 



