S70 PHYSIOLOGY. 



strongly. And in apoplexy the pulse is often strong, when 

 the heart acts feebly. Burns relates cases where the pulse 

 at the wrist did not correspond with the contractions of the 

 heart : and it cannot be denied that in some animals a cir- 

 culation exists, although they have no heart. Although fish- 

 es have a heart, their blood is moved through the body by 

 vessels. After the heart is taken out of the body, the blood 

 is still seen to flow in the small vessels. 



36. I have stated that arteries contract by an irritating 

 substance being applied to them. Hartshorn, or ammonia, 

 will make an artery shrink so as to lose one eighth of its cir- 

 cumference. A partial enlargement of an artery takes place 

 in a living animal by exposing it, and rubbing it between 

 the finger and thumb, but in general no pulsation will be 

 seen in an artery thus exposed. 



37. The capillary vessels have an action independent of 

 the heart. When the blood has reached the ends of the ar- 

 teries, or the capillary vessels, the force of the heart and ar- 

 teries is probably nearly, if not quite exhausted. Dr. Ar- 

 nott says that the blood is driven into them, by a force 

 equal to four pounds to the square inch. There is no doubt 

 that the action of the heart is sufficient to force the blood 

 through the arteries into the veins ; for when the heart acts 

 feebly the surface of the body is pale and cold. But the 

 blood is known to move in a backward or retrograde direc- 

 tion. When a leech is applied to the skin, the blood flows to 

 the spot from all quarters. In blushing, the capillaries of 

 the cheek dilate instantly and admit more blood ; under the 

 influence of fear they contract, and the face becomes pale ; 

 tears will gush from the eye in a moment and suddenly dis- 

 appear ; now all these things could not happen if these ves- 

 sels did not act independent of the heart. 



38. It is probably capillary action which moves the fluids 

 in all animals that have no heart. Persons have lain in a 

 swoon apparently dead for days together and then revived. 

 In these cases life was preserved in the capillary circulation, 



