MOVEMENT OF THE BLOOD IN THE CAPILLARIES. 



343 



pressure in the arteries, reaches its greatest intensity. The closure of the 

 sigmoid valves exerts little influence on the rapidity. The rapidity is great- 

 est during expiration, and least during inspiration. Section of the spinal 

 cord in the atlo-occipital region, or of the Pneumogastrics, increases both 

 the speed of the blood and the pressure in the arteries. On ligature of one 

 carotid the rapidity of the blood was found to increase in the other. 



4. Movement of the Blood in the Capillaries. 



260. In Man, as in all the higher Animals in the adult condition at 

 least the Capillary circulation is almost entirely carried on through tubes 

 having distinct membranous parietes, the only known exception being in the 

 case of the spleen ( 157, ii). 1 These lubes commonly form a minutely- 

 anastomosing network (Fig. 150), into which the blood is brought by the 

 ramifications of the arteries on one side, and from which it is returned by 



FIG. 150. 



Capillary plexus in a portion of the web of a Frog's foot, magnified 110 diameters: 1, trunk of vein ; 



2, 2, 2, its branches; 3, 3, pigment cells. 



the radicles of the veins on the other. The walls of the tubes are com- 

 posed of a delicate membrane, on the inner surface of which is a single layer 

 of epithelial cells possessing nuclei, and of fusiform shape, in this respect 

 resembling the cells lining the smaller arteries, but differing from those in 

 the interior of the veins, which are lozenge-shaped, with wavy outline. 

 According to Eberth' 2 (Fig. 151), the walls of the very finest capillaries, as 



1 The capillary circulation may be well seen in the web of the foot, in the lung, 

 mesentery, and tongue of the frog, the tail of tadpoles and of fi>h (see Caton, Quart. 

 Journ. of JVlic. Science, 1870, p. 236), and in the peritoneum of mammals by the 

 plan suggested by Strieker and Burdon-Sanderson, in which a guinea-pig is chloral- 

 ized, the abdominal cavity opened, and the omentum floated in a warm bath con- 

 taining common salt in solution. (See Quart. Journ. of Mic. Sci., Oct. 1870.) 



2 Wurzbiirg. Naturwiss. Zeit. , Bd. vi, 1805, p. 27, and StricUer's Hum. and Comp. 

 Histology, Syd. Soc. Trans., Art. Bloodvessels. See also Chrzonszczewsky, Vir- 



