CHAPTER VI 



THE FROG (continued) : THE VASCULAR SYSTEM THE 



CIRCULATION OF THE BLOOD 



IN our preliminary examination of the frog (Chap- 

 ter II) we learned one or two facts about the vascular 

 system. We found that there is a heart within a 

 pericardium, two sets of vessels, arteries and veins, 

 containing red blood, and a set of irregular cavities or 

 sinuses, containing lymph. We must now try to get 

 some more accurate and detailed information on these 

 matters. 



General Characteristics of Blood and Lymph. It will 

 be convenient to begin by studying certain easily verified 

 characteristics of the blood. Frog's blood may be used, 

 or, as it is as well to have a considerable quantity, that 

 of some larger, freshly-killed, red-blooded animal, such 

 as a rat or rabbit . 



When first drawn from the heart or vessels the blood 

 will be seen to be a fluid, nearly as mobile as water or 

 milk ; it " finds its level," like any other liquid, and can 

 be readily poured from one vessel to another. In a few 

 minutes, however, it undergoes a change ; it ceases to 

 be fluid, and coagulates, or " sets " into a jelly, which, if 

 turned out of the vessel, retains the shape of the latter. 

 Before long a further change takes place ; the jelly 



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