LECTURE IX 

 CIRCULATION 



Blood. — This is a complex fluid consisting of serum, fibrin 

 factors, and two kinds of corpuscles — the red and the white. 



Serum is the watery, straw-colored, fluid portion of the blood 

 less the fibrin (clot) factors. It contains various nutrient and 

 waste materials, including oxygen and carbon dioxid gases, 

 mineral matters and many inorganic compounds. 



The fibrin factors are fibrinogen and an enzyme. AVhen blood 

 is exposed to the air or comes in contact with a foreign surface, 

 the fibrinogen is changed by an enzyme (thrombin) and forms 

 tiny threads of fibrin of which the clot is composed. Red cor- 

 puscles are entangled in the meshes, giving the red color. 



Red corpuscles are tiny discs, resembling in shape silver dollars 

 with the sides slightly concaved. Human corpuscles are about 

 1/3200 of an inch in diameter. About six in a row could be 

 placed across the end of a fine hair. They are born in the red 

 marrow of the bones, and die principally in the blood stream 

 and spleen. Apparently their chief function is to carry oxygen 

 from the lungs to the tissue cells. 



White corpuscles (leucocytes) are much fewer in number, and 

 are of several kinds, most of them larger than the red corpuscles. 

 They have the power of independent movement and may change 

 their own shape. The ratio in the blood of the horse is about 

 1 white to 500 red. White cells have their birth in various tis- 

 sues, like lymph gland, or adenoid tissue and bone marrow, and 

 some probably in the blood stream. Leucocytes have several 

 very important duties, such as destroying disease-producing 

 bacteria and aiding in the formation of blood clot and the ab- 

 sorption and distribution of fat as a nutrient. The temperature 

 of the blood in the various domestic animals ranges from 101 

 to 104°F. In the horse it varies from 100° to 101.5° ; in the 

 cow it is about 1 degree higher; in sheep it is from 100° to 

 104°. Its specific gravity is about 1060, and it constitutes about 



1/15 the body weight. 



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