330 PERIPHERAL NERVE FIBRES 



is distributed to them is much larger than in the nor- 

 mal condition. Besides this, the simple experiment 

 proves that the vessels are maintained for a long time 

 of a given calibre. Such a state of things can only 

 result from the influence of nerves which govern th 

 calibre of the small arteries ; and thus the quantity c 

 blood permitted to flow through them in a given tim: 

 is regulated and varied from time to time. Tb 

 mechanism is such that a small artery is made t 

 assume a different calibre, although this may be mo 

 mentarily altered by artificial means. I have shown 

 contrary to the statement of Kolliker, that all th 

 small arteries are abundantly supplied with nerves, 

 and that nerves, also ramify in the tissues external to 

 the capillaries, and upon the capillaries themselves. 



There are the two kinds of peripheral nerve-fibres 

 which take part in regulating the supply of nutrient 

 pabulum to every part of every tissue in the body : 

 I. The nerve-fibres distributed to the coats of 

 small arteries and veins which ramify upon, and 

 amongst, their muscular fibres. These are afferent 

 or motor. 2. The nerve-fibres distributed to the 

 capillaries, and in tissues which are altogether devoid 

 of capillaries. These are the afferent or excitor 

 branches and are connected with the centres from 

 which the vaso-motor nerves arise. These branches 

 have been demonstrated by me in many tissues, 

 and form a new system of nerve-fibres, not pre- 

 viously described. (See " Archives," No. xiii.) Now, 



