THE CIECULATION. 



739 



influences as will derange the circulatory system. The remark- 

 able energy of the circulation through the blood-vessels is very 

 finely illustrate'd by 

 spreading and ty- 

 ing apart the toes 

 of a frog's foot, and 

 examining the web 

 through a good 

 microscope. The 

 field of observation 

 will appear like an 

 immense plain cut 

 up with large riv- 

 ers intersected by 

 numerous small 

 streams, all run- 

 ning with the ra- 

 pidity of a torrent, 

 the larger currents 

 running much the 

 faster. The blood 

 corpuscles are also 

 clearly distinguishable. Something of an idea of this can be seen 

 by referring to Figs. 631 and 632, which represent such a view of 

 the circulation through the web. 



When the circulation is in its natural state, that 

 is, distributed properly to all parts of the body, it 

 implies a state of perfect health, but if, from any 

 cause, it is withheld or forced from any part of 

 the body, there is not enough blood in that part, 

 while there will be an excess in other parts. Thus, 

 if the horse is exposed to a cold wind, or is 

 chilled by a current of air striking the body, the 

 blood will be forced from its surface to the inter- 

 nal organs, accumulating where there is most free- 

 dom for it, or where it is weakest; usually in the 

 . lun ^ and surr ounding P arte > kidneys, bowels, 



Magnified 350 di- and sometimes in the feet, the first indication of 

 ameters. which would be a shivering fit, followed by fever. 



FIG. 629. Web of frog's foot stretching between two 

 toes, showing the blood-vessels and their anastomoses. 



a, a, Veins; 6, 6, 6, arteries, the capillaries 

 being between. 



FIG. 630. Epithe- 

 lial cells of 

 blood-vessels. 



a, &. From a vein; 

 c. From an artery ; 



