30G SPECIAL HISTOLOGY. 



or more, up to 0-02'" and 002 4'"; in diameter they measure 

 0-0004'" ; at the finest extremities, 0-0005 — 0-0008"'; on the 

 average, 00008 — 0-001'", at their origin from the lacuna. 

 Their true distance apart, in horizontal sections, in which they 

 appear as holes, is 00008 — 0-002"'; in transverse sections, in 

 which they produce the radiating striae, in consequence of their 

 being viewed in several planes, they appear to be somewhat 

 closer together, or at distances varying from 0-0008'" — 0-0012"'. 

 The circumference of a lacuna, together with the radiating 

 canaliculi belonging to it, forms an imperfect sphere, having a 

 diameter of from 0-02'" to 0-034'"; with reference to which, 

 however, it must not be forgotten, that individual canaliculi 

 transgress the usual length of the others, as I have, in fact, 

 measured anastomoses between two lacunae of the length of 

 0-04— 0-045'". 



The contents of the lacuna, according to the later investi- 

 gations of Donders, Virchow, and myself, appear very closely to 

 resemble those of the cells of cartilage during life; that is to say, 

 they are a clear, probably viscid fluid, with a nucleus. If bone- 

 cartilage be boiled in water or caustic soda for 1 or 2 minutes, 

 these nuclei often show themselves very distinctly; or opaque 

 corpuscles make their appearance, which must be regarded as 

 the contracted cell-contents including the nucleus, and analo- 

 gous to the corpuscles in cartilage. A peculiar phenomenon is 

 seen to occur, when bone is macerated in hydrochloric acid, 

 which was first noticed bv Virchow in a diseased, and afterwards 

 K n9 in healthy bone, and by myself in the 



, — _. cementum of the horse's tooth, — the 



/ , \ lacunae become isolated, having longer 



I- .l-Jfc^- \ or shorter processes, and appear like 



/^y^ydi— \ independent structures, or a sort of 



/J^Vij/ ~^-~ \ stellate cells. This phenomenon seems 



/M^-^^y^^ to depend simply upon the circumstance, 



^ '# v/// that the tissue immediatelv surround- 



^\Y m g the lacunae offers more resistance 



^ to the action of the acid than it 



does elsewhere. In the cementum of the horse's tooth, cells 



also enclosing the lacunae, and even Haversian canals, may 



Fig. 119. A bone spicule from an apophysis, with distinct lacunae and nuclei. 

 Boiled in water, and magnified 350 diameters. 



