208 



Human Physiology. 



I know of scarcely any spectacle more striking than a view ot 

 the circulation of blood in the capillaries of a frog's foot, as 

 seen under a powerful microscope. The blood rushes through 

 a net-work of sluices like mountain torrents, for the movement 

 is magnified as well as the size; and the red and white blood 

 globules look like oval cakes of ice in wintry streams. Fig. 52 

 gives a very good idea of the appearance of the vessels, but it 

 wants the colour and movement that make the natural object 

 so startling. 



Fig. 52. CIRCULATION IN A FROG'S FOOT. 



There are many interesting and important points about the 

 circulation of the blood. The muscular force of the heart is 

 sufficient, as is shown by the pulsations of our extremities, felt 

 at times to the ends of our fingers and toes, to send the blood 

 through the arteries, but not to force it through the capillaries, 

 where it seems to be influenced by capillary attraction, or the 



