and Laboratory Methods. 1177 



Of these the formo-picric of Weigert, and Flemming's, gave the best results. The 

 stains used were Benda's safranin and Hght green, Flemming's triple safranin- 

 gentian-orange, Mann's blue of toluidin-eosin ; especially good results were 

 given by Heidenhain's iron haematoxylin after the picric-formol fixative. All 

 sections were cut in paraffin. The author summarizes his results as follows : 

 As before stated, there is present in the larvae of Gastrophilus equi, Fabr, or 

 pecorum, Fabr. but not in those of Hypodenna bovis L. and Cephaloinyia ovis L., 

 an organ occupying the posterior fourth of the animal, having a characteristic 

 red color. This organ has anatomical continuity with the fat body. It is com- 

 posed of large cells, between which the tracheae branch and subdivide. The 

 smallest branches penetrate to the interior of these " tracheal cells." Nothing 

 further could be observed as to the ends of the branches beyond fine subdivision. 

 The cytoplasm of the cells is distinguished from the tracheal branches by the 

 different form and stain affinity of its filaments, which come into close relation 

 with the walls of the tracheae, but do not represent the fine continuations of these 

 tubes. These tracheal cells pass gradually over into adipose cells in the transi- 

 tion region of the organ. This transition is effected by filling the tracheal cell 

 with fat globules and the reduction of the intracellular trachea. Independent of 

 this tracheal organ, certain irregular subcutaneous tracheal cells are found in 

 certain regions of the body. The reason for this specialization is considered to 

 lie in the peculiar habitat of the larvae, since closely related forms living under 

 different conditions show no such structures. It is an example of limited adapta- 

 tion. Physiologically, the function of these cells is respiratory, and hence the 

 cells are really " cenocytes," differing however from the latter in a red instead 

 of a yellow coloration. The transformation of these tracheal cells into fat cells 

 argues for their " cenocytic " nature, and they represent the first step in respira- 

 tory differentiation. They are abundantly supplied with oxygen, and in conse- 

 quence easily elaborate fatty granules ; hence the functions of the two parts of 

 this organ are not distinct, but successive. a. m. c. 



Zollikofer, R. Kammerfiirbung der Leucocy- In the Study of leucocytes two objects 

 ten. Zeit. f. wiss. Mikros. u. f. Mik. Techn. . . , ^ . ^ . , . 



17: m-l2i iqoo. ^''^ ^'^ view, the fixation of the whole 



mass of them and the differentiation of 

 this mass into its different kinds. In order that the study may be done in a 

 counting chamber, it is necessary to mix the blood and the staining fluid, and to 

 have this mixture take place in one pipette. To determine the numerical rela- 

 tions of the different kinds of leucocytes on a cover-glass preparation is impos- 

 sible, since there is an unequal distribution of the kinds. Lymphocytes are 

 found in thick places of the film, and are rare or crushed in thin places. No 

 such objection can be made to a film of blood in a counting cell. The thing 

 needed was a diluting fluid for this " staining-chamber " which would render 

 the red corpuscles invisible and stain the white differentially. Thin aqueous 

 formalin solution answers the first requirement, and for a stain a mixture of 

 eosin and methylin blue (eosin W. G. and methylin blue B. x. of Griibler, Leip- 

 zig) was most satisfactory in the following composition : Eosin W. G. 0.05, con- 

 centrated formalin 1.0, distilled water 100.00; methylin blue 0.05, concentrated 

 formalin 1.0, distilled water 100.00. These solutions must be filtered; the 



