342 SPECIAL HISTOLOGY. 



diseases have microscopical researches afforded anything worth men- 

 tion here, except what has been made known by H. Meyer and myself 

 (11. cc.) with respect to ossification in rachitis. In this case I have 

 found : 1, that in the disproportionately large epiphysal cartilages, 

 the layer of the ossifying cartilage-cells (those disposed in rows), mea- 

 sured, instead of J, 2 to 5 lines ; 2, that the ossifying border is toothed, 

 owing to the circumstance that the cartilage and bone interlace in 

 various ways ; 3, and lastly, that in decidedly rachitic bones, the de- 

 position of calcareous granular particles is wanting, and the cartilage- 

 cells almost invariably, shortly before the matrix, and also without 

 any appearance of calcareous granules, are metamorphosed into bone- 

 cells, on which account the formation of the latter can, in no case, be 

 so well studied as in these bones (vid. supra}. Accidental cartilage- 

 and bone-formations are very frequent. The former tissue is met with, 

 notwithstanding that it is incapable of regeneration, and that wounds 

 of it heal only with a fibrous tissue, more rarely with bone (ribs), in 

 very many organs (bones, mammary glands, parotid, testicles, lungs, 

 and skin) forming what is termed enchondroma ; moreover, as a new 

 covering on the osseous growths, at the border of the worn articular 

 ends of bones (Ecker). The latter is seen in ossifications of the per- 

 manent cartilages (ribs, larynx, epiglottis, very rarely) of tendons 

 (exercir-knochen, for example), in the dura mater and arachnoid (Mies- 

 cher, Rokitansky), in the eye (Valentin), in the ovary, in fibrous 

 membranes (membrana obturatoria), in enchondroma, in fibrous and 

 carcinornatous growths, and in the lungs (Mohr's cysts containing hair). 

 Even in these cases the osseous tissue does not essentially differ from the 

 normal, and it is formed, sometimes from a cartilaginous, sometimes, 

 and in fact mostly, from a soft blastema (Yirchow, 1. c. p. 137). 



In investigations relating to the structure of bone, good sections are, 

 above all things, requisite. With a fine saw, thin slices are made, which 

 are ground with water upon a smooth stone with the finger, or with a 

 second smaller stone, for some minutes (5-10), until they are rendered 

 uniformly transparent. The sections are then cleaned, and (the fat, if 

 they contain any, being removed by ether) may be employed, being 

 wetted with water, for the study of the Haversian canals and disposition 

 of the lacunae ; and with turpentine, for that of the various lamellar 

 systems. The lacunae and their prolongations, which, in sections, are 

 dark and very distinct, owing to their being filled with air, are com- 

 pletely filled by thin turpentine, so that the latter in great part, and 

 also the former, are very frequently rendered invisible ; the same thing 

 happens in water and thicker turpentine, though less rapidly, whence, 

 before these agents have produced their effect throughout, many of the 

 lacunae and canaliculi are beautifully shown. If it be desired to pre- 

 serve the lacunae and canaliculi permanently visible, it is best to polish 

 a thin section, by rubbing it between two glass plates. It may then be 



