DR. BEAl-Ej ON THE TISSUES, 13 



and their tortuous course also receives explanation from tlie 

 factj that the particles first deposited become globules before 

 the process of ossification is far advanced. 



It may be said, that the growing matter extending from a 

 spore of mildew bores its way into the soft material, at the 

 expense of which it groAvs; but here this soft material is 

 clearly appropriated by the mildew, and becomes converted 

 into the germinal matter of the plant : but this process is 

 totally different from that by which canaliculi_,^are pro- 

 duced. 



A specimen of the so-called myeloid cells from one of the 

 cancelli of the bone of the great toe was next passed round. 

 Two or three of the masses are elongated and much bent. 

 These Dr. Beale believed might afterwards become ossified, 

 and form the spiculte of bone which form the imperfect septa 

 between the cancelli. Around these are many small granular 

 cells, and it is interesting to notice the fact, that while the 

 first structures are of a dark-red colour the latter are scarcely 

 tinged with the carmine, although both have been exposed to 

 its influence in the same way. The first is growing actively, 

 the last is comparatively inactive, and there can be no doubt 

 that it is being gradually removed as the former structure 

 advances. What remains will become the medulla. The 

 so-called myeloid cells are not peculiar to the cancelli and 

 the medullary membrane of bones, but they are also found 

 in the periosteum. Under ordinary circumstances many of 

 them gradually become converted into bone, but in disease 

 they increase in number rapidly, producing a soft, spongy 

 structure which only undergoes very imperfect ossification or 

 receives no calcareous deposit at all. In these so-called 

 myeloid cells the lecturer has not been able to distinguish 

 a cell-wall. Each mass is composed of a number of small 

 oval elementary parts, each of which consists of an oval mass 

 of germinal matter w'hich is faintly coloured, while the nucleus 

 is coloured dark-red Avith carmine. The germinal matter 

 gradually undergoes conversion into a soft-formed material 

 externally, which increases in thickness. Afterwards the 

 nucleus diminishes in size. In some cases the formed mate- 

 rial exhibits a somcAvhat fibrous appearance. 



Dentine. — There are fcAV anatomical questions. Dr. Beale 

 observed, which have given rise to more controversy, than 

 the structure and mode of formation of the dentine, and the 

 very last writer on the subject, M. Lent, describes the den- 

 tinal canals as consisting of direct processes of the whole 

 dentinal cells. " The matrix of the dentine is not formed of 

 the dentine cells, but is a secretion of these cells and of the 



