XXL THE BLOOD AND ITS CIRCULATION 



rrohlems, — To discover the coinpositioii ami uses of the (Uf- 

 f event parts of the blood. 



To find out the means by which the blood is circulated 

 about the body. 



Laboratory Suggestions 



Demonstration. — Structure of blood, fresh frog's blood and human 

 blood. Drawings. 



Demonstration. — Clotting of blood. 



Demonstration. — Use of models to demonstrate that the heart is a force 

 pump. 



Demonstration. — Capillary circulation in web of frog's foot or tadpole's 

 tail. Drawing. 



Home or laboratory exercise. — On relation of exercise on rate of heart 

 beat. 



Function of the Blood. — The chief function of the digestive 

 tract is to change foods to such form that they can be absor])ed 

 through the walls of the food tube and become part of the blood. ^ 



If we examine under the microscope a drop of blood taken from 

 the frog or man, we find it made up of a fluid called plasma and two 

 kinds of bodies, the so-called red corpuscles and colorless corpuscles, 

 floating in this plasma. 



Composition of Plasma. — The plasma of blood is found to be 

 largely (about 90 per cent) water. It also contains a considerable 

 amount of protein, some sugar, fat, and mineral material. It is, 

 then, the medium which holds the fluid food that has been ab- 

 sorbed from within the intestine. This food is pum])(Ml to the body 

 cells where, as work is performed, oxidation takes i)lace and heat 

 is given off as a form of energy. The almost constant temperature^ 



1 This change is due to the action of certain enzymes upon tht' nutrii'iit.s in va- 

 rious foods. But we also find that peptones are changed back again to proteins wlu-n 

 once in the blood. This appears to be due to the reversible action of the enzymes 

 acting upon them. (See page 307.) 



313 



