59 
probable Action in Health and Disease. 
The results of these experiments, considered in connection with 
the facts discovered hy careful anatomical investigation, prove, I 
think, conclusively the function of the fine nerves distributed to the 
capillary vessels, and indicate the precise manner in which they act. 
In many tissues and organs in which the circulation is readily 
disturbed by peripheral irritation the nerve fibres distributed to 
capillary vessels are exceedingly numerous. 
Arrangement of Self-acting Mechanism by which the Supply of 
Blood to Tissues is regulated. 
We are now in a position to consider the probable arrangement 
of the reflex nerve mechanism by which the flow of blood in the 
capillaries is regulated, and the equable distribution of nutrient fluid 
to the tissues outside the capillaries ensured in a state of health. 
We shall also see how this elaborate mechanism is rendered self- 
acting, self-regulating, and self-adjusting during the healthy state. 
The nutritive operations of man and many vertebrata have to 
be carried on with comparatively little alteration under very variable 
and continually changing external conditions. A limited range of 
variation is permitted, hut if the limits within which this self- 
adjusting apparatus acts perfectly, he overstepped in either direction, 
as not unfrequently happens under the very variable and artificial 
conditions to which civilized man and domestic animals are exposed, 
the range of the capacity for self-adjustment is exceeded, and a part 
of the mechanism is temporarily damaged or actually destroyed. 
Unfortunately repair can only be imperfectly carried out, and 
the mechanism restored to its normal state in cases in which the 
derangement is comparatively slight. So complex is the apparatus 
and so widely distributed are its interdependent parts that renovation 
after its destruction is complete is impossible, and I doubt if its 
re-formation in the adult has ever occurred, or is indeed possible. 
In the diagram appended I have put together the facts I have 
ascertained by anatomical investigation, and have represented the 
several parts of which the self-regulating mechanism is, I believe, 
made up. I have also indicated what I believe to be their true 
relationship.* 
* The artery a is surrounded by muscular fibre cells which are supposed to be 
contracted, and the capillaries near the artery over the figure 2 are also represented 
as they would appear when very little blood was traversing them ; while those to 
the left of the drawing, over figure 1, are as they would appear if distended with 
blood. It is obvious that in the first case an interval would exist between the 
nerve fibres and the capillary vessels, while in the latter, where the capillaries 
are distended, the external surface of their walls would be almost in contact with 
the nerve fibres and the particles of bioplasm connected with them. A dark line 
on each side of the artery indicates the diameter of the vessel when its walls are 
relaxed, and similar dark lines within the dilated portion of the capillary vessels, 
over figure 1, show the diameter of these vessels when the flow of blood through 
the artery is checked by the contraction of its muscular coat. 
VOL. VIII. 
F 
