178 THE HUMAN BODY. 



fact has often been used to further the ends of justice in 

 determining whether spots of blood on the clothes of a 

 suspected murderer were really due to the cause assigned 

 by him. The red blood-corpuscles of birds, reptiles, amphi- 

 bians, and fishes cannot be confounded with those of man, 

 since they are oval and contain a nucleus in the centre such 

 as is not found in our red corpuscles. 



Haemoglobin. Each red corpuscle is soft and jelly like. 

 Its chief constituent, besides water, is a substance called 

 licem' -o-glo f -bin, which has the power of combining with 

 oxygen when in a place where that gas is plentiful, and of 

 giving it off again in a region where oxygen is absent or 

 present only in small quantity. Hence as the blood flows 

 through the lungs, which are constantly supplied with fresh 

 air, its corpuscles take up oxygen, which, as it flows on, is 

 carried by them to distant parts of the body where oxygen 

 is deficient, and there given up to the tissues. This oxygen- 

 carrying is the function of the red corpuscles. 



Arterial and Venous Blood. Haemoglobin itself is dark 

 purplish-red in color; haemoglobin combined with oxygen 

 is bright scarlet red. Accordingly, the blood which flows to 

 the lungs after giving up its oxygen is dark red in color, 

 and that which, having got a fresh supply of oxygen, flows 

 away from the lungs is bright scarlet. The bright red blood 

 is called arterial and the dark red venous. 



Can the blood of most mammals be certainly distinguished from 

 human blood ? Point out a use which has been made of this fact. How 

 do the red corpuscles of birds, reptiles, and fishes differ from human? 



Describe the consistence of a red corpuscle. What are its chief 

 constituents? Point out an important property of haemoglobin. How 

 does this enable it to receive and distribute oxygen? What is the 

 function of the red corpuscles? 



What is the color of haemoglobin? What of haemoglobin com- 

 bined with oxygen? What is the color of blood flowing to the 

 lungs? Why? The color of that flowing from the lungs? Why? 

 What is arterial blood? What venous? 



