108 



BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



same length of time in a one-half per cent solution of hfematoxylin. 

 Decolorization was effected by the two per cent mordant, the process 

 being controlled under the microscope. 



This stain gave the best results both for the structure of the nerve 

 cells and for mitotic figures in the regenerating tissues. No advantage 

 was found to be gained by using safranin in combination with the 

 hematoxylin. From what has been said, then, it follows that fixation 

 in Flemming's mixture, followed by the iron-hsematoxylin stain, proved 

 to be the best combination. 



Gentian violet was used to obtain sharp selection of kinetic chroma- 

 tin, but it was useless for finer cytoplasmic structure. Kernschwartz 

 gave results similar to those obtained by the iron-haematoxylin, but 

 inferior in clearness. One sublimate series was stained in Kernschwartz 

 and safranin with fairly good results, especially as to some cells of the 

 regenerated epidermis (Figures 44 and 45). 



Whatever the stain used, the best demonstration of the "centro- 

 some " and cytoplasmic fibrill^B was obtained when the stain had been 

 well extracted from the cytoplasm. In heavily stained cells the fiuer 

 structures were made out with much greater difficulty. 



5. Drawings. 



The preparations were studied with a Zeiss ^ oil immersion and 

 Zeiss achromatic oculars 3 and 4. The drawings were made with the 

 aid of an Abbe camera. Attention is called to the fact that all the 

 drawings of cells and mitotic figures are to the same scale, a magnifi- 

 cation of 2000 diameters. The outlines of cells, nuclei, and nucleoli 

 were traced with the aid of the camera. Generally the "centrosome" 

 and prominent granules could also be located, but only in rare cases 

 could the radiations represented in the figures be seen with the camera 

 in place. The figures are reproduced from pencil drawings. 



A diagrammatic treatment of the drawings was avoided as far as pos- 

 sible, and it was attempted rather to reproduce, as accurately as could 

 be, the appearances seen in the preparations. The drawings were 

 reproduced by the heliotype (gelatine) process because by it a more 

 accurate reproduction of the relative conspicuousness of the structures 

 represented in the drawings may be obtained than by the lithographic 

 process. It must be understood, however, that in the figures of nerve 

 cells the conspicuousness of the radiating systems is slightly exag- 

 gerated. These lines catch the eye more readily in the printed figures 



