BLOOD-PL A SMA . 137 



they cannot be readily distinguished; but in most cases 

 the size is sufficiently different to enable a safe opinion 

 to be formed, with a little pains. This 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 stated by him. 

 The red blood-corpuscles of birds, reptiles, amphibians, 

 and fishes, cannot be confounded with those of man, 

 since they are oval and contain a little mass in the cen- 

 tre, which pushes out their sides and makes them pro- 

 ject, instead of being hollowed. 



9. The Use of the Red Corpuscles is to carry oxygen over 

 the body. When blood flows through the lungs, these 

 corpuscles take oxygen (Chap. XV.); as it flows through 

 other organs they give up that gas to them. When the 

 corpuscles are laden with oxygen their color is bright 

 red, if a number of them be seen closely packed to- 

 gether; and when they have given up their oxygen, it is 

 dark red. The different quantity, of oxygen in the red 

 corpuscles, is thus the reason of the different colors of 

 arterial and venous blood. 



10. The Blood-Plasma consists of water with a good 

 many things dissolved in it. The most important of 

 these are (i) albumens; (2) sugar; (3) minerals. The 

 plasma has also floating in it many very small drops of 



Exceptions? How may they be distinguished in most cases? How 

 has this been used to further the ends of justice? Describe the red 

 corpuscles of birds, etc. 



9. Use of the red corpuscles ? When do they receive oxygen ? 

 When give it up? How does oxygen affect their color? Why do 

 arterial and venous blood differ in color ? 



10. Of what does blood plasma consist? The most important 

 things dissolved in it? Floating in it? What does the plasma con- 

 tain in addition to nourishing substances ? 



