SYSTEMATIC SYNTHESIS OF TISSUES INTO ORGANS. 371 



circulate it rapidly around the roots of the hair can pro- 

 mote its growth. 



1154. Remark. The various lotions and nostrums that are sold to 

 promote the growth of the hair can have no other effect than to increase 

 the circulation of Blood, and this the brushing alone would do equally 

 as well. Some are said to prevent dandruff ; that is only the external 

 layer of scales, and ought to come away. 



1155. THE NAILS are only the cells of the external 

 layer of the skin, with an increased quantity of horny 

 matter deposited in them, and modified in a few other 

 particulars. 



FIG. 250. FIG. 251o 



Fig. 249, vertical section of finger-end. 1, cuticle; 2, where it turns 

 back to become continuous with the nail, 3 ; 4, cuticle leaving nail ; 5, 6, 

 7, 8, surface of the dermis or first layer of cuticular cells ; 9, 10, 11, 12, 

 dermis or true skin. 



Fig. 250 represents the surface (matrix) on which the nail grows ; 1, 

 being the skin overlaying the back edge or root of the nail ; 2, a portion 

 of 1 turned back ; 3, shows less vascular part, and 4, the more vascular. 



Fig. 251 represents the under surface of a nail, grooved to fit the 

 matrix. 



1156. THE NAILS GROW forward from the root at the 

 same time that additional cells are applied from below, 

 increasing their thickness toward the front part. 



SECTION X. 



MODIFICATORY ORGANS. 

 Blood- Cells. 



1157. Remark. BLOOD-CELLS cannot, properly speaking, BE CALLED 

 ORGANS, since an organ is constructed of several tissues, and is under 

 nervous influence ; while Blood-cells are constructed of a single secretory 



1154. What said of nostrums, etc.? 1155. What are? Describe Fig. 249. 

 Fig. 250. Fig. 251. 1156. How do ? 1157. Why cannot ? How considered? 



