THE BLOOD. 55 



of the permanent teeth of course takes place long before the 

 cutting of those which they are to succeed; one of the first 

 acts of the newly-formed little dental sac of a milk-tooth being 

 to set aside a portion of itself as the germ of its successor. 



The following formula shows, at a glance, the comparative 

 arrangement and number of the temporary and permanent 

 teeth : 



MO. CA. IN. CA. MO. 



f Upper, 21412 =10 



Temporary Teeth,. . \ =20 



(Lower, ^21412 =10 



MO. BI. CA. IN. CA. BI. MO. 



(Upper, 321412 3 = 16 



Permanent Teeth,. . \ - =32 



(Lower, 3 2 1 4 1 2 3 = 16 



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 tem- 

 porary 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, un advisable 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 therefore at once proceed 

 to consider the structural and chemical composition of this 

 fluid. 



Wherever blood can be seen under a moderately high micro- 

 scopic power as it flows in the vessels of a living part, it appears 

 a colorless fluid containing minute colored particles. The 

 greater part of these particles are red, when seen en masse, 

 and they are the source of the color which, so far as the naked 

 eye can see, belongs to every part of the blood alike. The 

 colorless fluid is named liquor sanguinis ; the particles are the 



