THE CELL DOCTRINE. 147 



and are almost fantastic in their irregularity, ex- 

 hibiting also prolongations which unite with those 

 of neighboring bone-cells, and with the Haversian 

 canals which conduct the bloodvessels through bone. 

 The shape of the cells through whose agency the 

 teeth are formed is also seen to be peculiar, those 

 whence the dentine is developed being provided with 

 a single long process, giving an eleventh form of cell. 

 Those producing the enamel are columnar, while the 

 crusta petrosa, or portion of bone-like substance cover- 

 ing the fang, contains cells similar to those of bone. 

 Finally, the cells of adipose or fatty tissue require 

 allusion. They are spherical or compressed vesicles 

 or sacs of considerable size, are filled with oil, and 

 exhibit in consequence a brilliant, highly refracting 

 character, under the microscope, indicated by a broad 

 dark border and a transparent centre. In the begin- 

 ning they are in no way dilferent from other young 

 cells, but, according to Beale, their bioplasm, instead 

 of being converted into the ordinary non-germinal 

 matter of albuminous composition, undergoes a fatty 

 conversion, in the course of which it gradually di- 

 minishes in size and is thrust towards the wall of 

 the cell, where it may sometimes be demonstrated 

 by staining as a small flattened nucleus. The oil 

 thus produced is termed by Beale secondary formed 

 material, to distinguish it from the albuminous non- 

 germinal matter. The same term is applied by him 

 to the secondary product, starch, found in the shape 

 of concentrically laminated granules in many vegeta- 

 ble cells. According to most other histologists, how- 

 ever, the fatty contents of the /a<- vesicles are an infil- 



