THE CIECULATION. 



739 



influences as will derange the circulatory system. The remark- 

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

 finely illustrated 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 plaiu cut 

 up with large riv- 

 ers intei-sected by 

 numerous small 

 streams, all run- 

 ning with the ra- 

 pidity of a torrent, 

 the laro-er currents ^^^' ^^^---^^^ °^ ^''og's foot stretching between two 



. ^ toes, showing the blood-vessels and their anastomoses. 



runnmg much the 



faster The blood **' **' ^^^°^ ' ^' ^' ^' ^'■*^^"^^' *^° capillaries 



being between, 

 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 



Fig. 630.-Epithe- i^j^^j ^-^ ^^ f^^.^^^i ^^^^^ ^^^ surface to the inter- 

 nal organs, accumulating where there is most free- 

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

 lungs and surrounding parts, kidneys, bowels, 

 and sometimes in the feet, the first indication of 

 which would be a shivering fit, followed by fever. 



lial cells of 

 blood-vessels. 



a, b. From a vein; 

 c. From an artery; 

 Magnified 350 di- 

 ameters. 



