328 ' SELF-KEGULATING MECHANISE. 



gation, 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. By reference to the 

 plan the reader will observe that the artery a is sur- 

 rounded 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 attained by 

 these vessels when the flow of blood through the 

 artery is checked by the contraction of its muscular 

 coat. 



Such an arrangement as that represented we 

 should find would act as a self-regulating mechanism 

 of the most perfect kind. Suppose for a moment a 

 tissue is receiving more nutriment than it appro- 

 priates, the capillary nerve fibre will be at once dis- 

 turbed, a change instantly transmitted to ihe nerve 

 centre, and the efferent nerves distributed to the 

 artery participating, the muscular fibres will contract. 

 The arterial tube will be instantly narrowed, and less 

 blood consequently sent to the tissue. In an opposite 

 state the phenomena would be reversed the arterial 

 walls relaxed and the capillaries distended with blood. 

 Or suppose that any noxious materials or living 

 germs of any kind were making their way from with- 



