256 Dr. Beale Croonian Lecture. [May 11, 



the nervous nature of the fibres distributed to muscle itself; indeed, if these 

 fibres distributed to the capillaries are not nerve-fibres, none of the fine 

 fibres in the cornea, fibrous tissue, &c. already alluded to and represented 

 in my drawings, are nervous. Fine nerve-fibres can be followed from the 

 nerve-trunk, and traced to their distribution on capillary vessels, as repre- 

 sented in this drawing, and as I have also shown to be the case in my 

 Memoir " On the Papillae of the Frog's Tongue," presented to the Royal 

 Society in June 1864. Some of the fibres can be traced from the imme- 

 diate neighbourhood of the capillary, where they for the most part ramify, 

 in the surrounding tissue, and may be followed to the point where they 

 pass into undoubted nerve-trunks. 



With reference to the office performed by these nerve-fibres, a care- 

 ful consideration of all the facts I can ascertain in connexion with 

 this question, leads me to the conclusion that these fibres, close to the 

 capillary vessels and in tissues destitute of capillaries, are not concerned 

 in special sensation, but are the afferent fibres to the nerve-centres in 

 which the efferent fibres distributed to the small arteries take their rise. 

 I believe that these fibres do exert an influence upon the process of 

 nutrition, but only by their indirect influence upon the nerves which govern 

 the calibre of the small arteries transmitting the nutrient fluid to the 

 capillaries nearest to the tissues in which they ramify. 



Although time precludes me from entering into this part of the inquiry, 

 I may be permitted to allude briefly to the mechanism which I believe is 

 concerned in regulating the nutritive process, as it occurs in the tissues of 

 man and those higher animals whose nutritive operations continue to be 

 carried on with comparatively little alteration under very varying external 

 conditions. The arrangement I am about to describe appears to be, within 

 a certain range of variation, self-adjusting. If, however, the limits be 

 overstepped in either direction, as not unfrequently happens, under the 

 very artificial conditions to which man and many of the domestic animals 

 are exposed, the range of self-adjustment is exceeded, and oftentimes a 

 part of the mechanism is completely destroyed and can never again be 

 effectually repaired or replaced. 



It is obvious that the afferent fibres above referred to, must be affected 

 by any alterations occurring in the flow of pabulum to the tissue in their 

 immediate neighbourhood. Suppose, for example, the quantity of nutrient 

 pabulum flowing to the cells of a tissue to which nerve-fibres of this class 

 are distributed, to be unusually great, these nerve-fibres would necessarily 

 be compressed by the swelling of the surrounding elementary parts which 

 absorb the pabulum. This pressure would, in the first instance, so affect 

 the nervous centre as to cause a change in the condition of the efferent 

 nerve-fibres, which would induce contraction of the small arteries trans- 

 mitting the blood to the capillary vessels, and thus the quantity of pabulum 

 sent to this locality would be immediately reduced. The nuclei of the 

 nerve-fibres would also participate in the increased absorption of nutrient 



