56 THE BLOOD. 



From this formula it will be seen that the two bicuspid 

 teeth in the adult are the successors of the two molars in 

 the child. They differ from them, however, in some 

 respects, the temporary molars having a stronger likeness 

 to the permanent than to their immediate descendants, the 

 so-called bicuspids. The temporary incisors and canines 

 differ but little, except in their smaller size, from their 

 successors. 



CHAPTER V. 



THE BLOOD. 



ALTHOUGH it may seem, in some respects, unadvisable to 

 describe the blood before entering upon the physiology of 

 those subservient processes which have for their end or 

 purpose its formation and development, yet there are 

 many reasons for taking such a course, and we may there- 

 fore at once proceed to consider the structural and chemical 

 composition of this fluid. 



Wherever blood can be seen under a moderately high 

 microscope-power as it flows in the vessels of a living part, 

 it appears a colourless fluid containing minute coloured 

 particles. The greater part of these particles are red, when 

 seen en masse, and they are the source of the colour which, 

 so far as the naked eye can see, belongs to every part of the 

 blood alike. The colourless fluid is named liquor sanguinis ; 

 the particles are the Hood corpuscles or blood-cells. The struc- 

 tural composition of the blood may be thus expressed : 



Liquid Blood 



Liquor Sanguinis J Fibrin 



or Plasma. ( Serum 



When blood flows from the living body, it is a thickish 

 heavy fluid, of a bright scarlet colour when it comes from 

 an artery ; deep purple, or nearly black, when it flows from 



