PLATE XXI. MECHANISM GOVERNING THE DISTRIBUTION OF 

 BLOOD IN THE CAPILLARIES. 



Diagram to show self- regulating mechanism connected with the minute arteries and 

 capillaries, a, artery with muscular fibre cells ; the dark lines show its diameter when 

 dilated, b, small vein, c, capillary network. Over No. 1 the capillaries are dilated, 

 and over No. 2 they are contracted, d is a ganglion cell with at least two sets of nerve 

 fibres connected with it, one of which, e, divides and subdivides, giving off nerve-fibres 

 which are distributed to the artery a, "while the other,^ is continuous with the plexus 

 of nerve fibres ramifying close to the capillary vessels. Nerve fibres are also dis- 

 tributed to the smatt vein, 6, but these are not represented in the drawing. The bio- 

 plasm of the vessels and nerve-fibres is shown, p. 327. 



[329 



