DEPARTMENT OF EMBRYOLOGY. 109 



that pyrrhol cells occur in regions where bone is developing, and are most 

 numerous in areas where the resorption of bone and cartilage is most 

 active. It may therefore be considered that they take some part in 

 this process, and it is beheved that they ingest the debris and assist 

 in clearing it away. The osteoblast is not trypanophilic and hence 

 must be excluded from the class of pyrrhol cells and their derivatives, 

 such as the foreign-body giant cell. The same authors used the vital- 

 staining method, combined with Spalteholz's clearing method, for the 

 demonstration of centers of osteoblastic activity. The epiphyseal and 

 apophyseal centers, colored in deep blue, are soon embedded in their 

 transparent cartilaginous matrices. The growing ends of the diaphysis 

 are much more darkly stained than the remainder of the bone shaft. 

 The unique feature of this method is that it demonstrates clearly the 

 different ossification areas, even before the process of deposition of 

 calcium salts has occurred to any marked degree. In centers where, 

 by former methods, the new bone is almost, if not quite, invisible, 

 owing to the small amount of calcium present, this method brings out 

 the seat of ossification quite distinctly. 



Dr. G. B. Wislocki describes a new technique, in combination with 

 Clark's method and sections, for studying the growth of lymphatics. 

 It consists in vitally staining amphibian larvae and observing the lym- 

 phatics, whose endothelium stains quite specifically intra vitam with 

 acid-azo dyes. With this method the growing lymphatics were readily 

 studied, as the lymphatic endothelium was distinguishable at all 

 times from mesenchyme cells or vascular endothelium, owing to its 

 characteristic stain. Wislocki also studied the behavior of trypan blue 

 injected into the peritoneal cavity of teleosts. After a few hours there 

 appears a gradually developing blue coloration of the integument. 

 The benzidine dyes are phagocytized by the endothelium of the hepatic 

 sinuses, analogous to the Kupffer cells in mammals, and by the reticulo- 

 endotheUum of the spleen, as also by the endothehum of the renal 

 portal system. There is furthermore a widespread storage of vital 

 dye on the part of the endothelium of the lymphatic vessels, a condition 

 also noted in amphibian larvse, but never known to occur in manmials. 



