VESSELS OF AN INFLAMED PART. 423 



sure is withdrawn, the redness recurs, and exhibits 

 precisely the same tint as before. From this it is clear, 

 not only that the capillaries are unduly distended, 

 but that the calibre of the small arteries through 

 which the blood is distributed to them is much larger 

 than in the normal state. Besides this, we are able to 

 prove by this simple experiment that the vessels may 

 be maintained for a long time of a given calibre. v Such 

 a state of things can only result from a certain regu- 

 lated but definite influence upon nerve-centres which 

 govern the calibre of the small arteries (p. 330). The 

 temporary change induced in the nerves can be main- 

 tained at one definite degree for a considerable time 

 In this way the quantity of blood permitted to flow 

 through the capillaries in a given time is regulated and 

 varied within certain limits. The mechanism is such 

 that a small artery is made to assume and to retain for 

 a longer or shorter period a different calibre, although 

 this may be momentarily altered by artificial means. 



Now I believe that the alcohol passes through the 

 walls of the capillaries, and acts directly upon the 

 nerves, which I have shown are distributed just exter- 

 nal to them.* By these afferent nerves the nerve- 

 centres are influenced, and in consequence, the 

 intensity of the current transmitted by the vasa- 

 motor nerves of the small arteries is modified. That 

 alcohol affects the nervous system very readily is 



* $>zz Archives of Medicine, No. xiii. Phil. Trans., 1863. Monthly 

 Microscopical Journal, Jany. 1872. 



2 F 2 



