CHAPTER II. 



THE BLOOD. 



The special function of the blood is to nourish the tissues 

 and to assist in removing from them the products of their 

 activity. To enable this to be carried out, the blood is 

 exposed in the lungs to the oxidizing action of the atmo- 

 sphere, whereby the fluid which has recently been going 

 the round of the body, and is highly charged with dele- 

 terious products, is once more revivified. 



By means of a peculiar channel the circulation is placed 

 in direct communication with the nourishing fluid absorbed 

 into the body from the intestinal canal, by which process 

 the blood is being constantly renewed. 



Blood consists of a fluid portion known as the liquor 

 sanguinis, floating in which are an immense number of 

 solid particles known as corpuscles ; it is the object of this 

 chapter to point out how the liquor sanguinis and corpus- 

 cles are composed, and their various duties in the system. 



Physical Characters of the Blood. — The colour of blood 

 varies cither as it is drawn from an artery or a vein : in 

 the former it is of a, bright scarlet colour, whilst in the latter 

 it is of a bluish or purplish red. The colour of blood is 

 due to a peculiar crystalline proteid known as haemoglobin, 

 and depending upon the condition of oxidation in which 

 this is found is the scarlet or purplish colour obtained. 

 Blood is opaque, owing to the manner in which the mr 

 puscles found in it reflect, the light, when these are destroyed 

 the fluid becomes transparent; the liquor sanguinis is of a 

 yellow colour. 



