CHAPTER IV. 



BLOOD. 



THE blood may be looked upon as the common carrier of the 

 body. It serves to carry food stuffs to the tissues from the aliment- 

 ary canal where they have been absorbed and O and CO, be- 

 tween the lungs and the tissues. It also carries away from the tis- 

 sues waste products, resulting from their metabolism, to the organs 

 of excretion. It acts as a medium of exchange between the tissues 

 themselves, carrying products of glandular activity from one group 

 of cells to another, as in the internal secretions. It is a prime factor 

 in the regulation of body temperature. It is finally, in part, the re- 

 ceptacle for and, in part, the seat of the formation of protective 

 substances which are manufactured by the body as a result of the 

 introduction of toxins from without. 



In structure, the blood consists of two main elements, a liquid 

 portion or plasma, and a cellular portion, corpuscles. The latter 

 are divisible into two classes, the colored corpuscles or erythro- 

 cytes and the colorless corpuscles or leucocytes. They are also 

 known respectively as the red and white corpuscles. Their num- 

 bers, varieties, and properties will be considered later. 



I. COAGULATION OF THE BLOOD. 



Narcotize and etherize a dog or rabbit. The former will furnish 

 more blood. Expose both carotid arteries. Introduce a cannula 

 into each carotid, securing the arteries on the side near the heart 

 with artery clamps. 



i. Prepare a series of test tubes, as follows: (a) Clean empty 

 tube for receiving a sample of fresh shed blood; (b) tube half full 



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