106 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



Material was left in the fixing fluid for from five to forty-eight hours. 

 A longer or shorter time within these limits gave no appreciable differ- 

 ence in results. The objects were then washed in distilled water for 

 about twenty-four hours, then passed through ascending grades of 

 alcohol, cleared in cedar oil and imbedded in paraffin. 



Hermann's acetic-osmic-platinic chloride mixture was used with good 

 results, although it seemed to be in no way superior to the Flemming 

 mixture. The Flemming preparations gave a rather better quality of 

 stain with Heideuhain's iron-hsematoxylin. The method of treatment 

 with Hermann's fluid was similar to that just described for Flemming's 

 fluid. 



Vom Eath's picric-osmic-acetic-platinic chloride gave no results of 

 value. The after treatment with crude pyi'oligneous acid was used as de- 

 scribed by vom Rath ('95). In some cases a two per cent solution of pyro- 

 gallic acid was substituted for the pyroligneous, with similar results. 

 The length of time of the after-treatment, during which the reduction of 

 the platinic chloride takes place, was varied, but in all cases the cytoplasm 

 was blackened to such an extent that it became too opaque for the 

 observation of the exceedingly delicate structures revealed by other 

 methods. In some preparations mitotic figures were brought out with 

 remarkable clearness by this method, especially as to the sharpness of 

 spindle fibi'es, but, for the observation of polar and cytoplasmic struc- 

 tures, fixation in Flemming's or Hermann's fluid followed by a regressive 

 stain gave results far superior to those obtained by a method which 

 depends upon the deposition of a metallic salt in the cell structures. 



Corrosive sublimate in a saturated aqueous solution containing one 

 per cent of acetic acid was used with results which corroborated those 

 obtained by the Flemming and Hermann fluids as to cytoplasmic 

 structures in the ganglion cells, but the demonstration of these struc- 

 tures was far inferior to that obtained by the other methods. The sub- 

 limate failed to bring out the finer structure of the cytoplasm as clearly 

 as the osmic mixtures. Radiating fibres were very indistinctly shown. 

 The sublimate gave decidedly inferior results in the demonstration of 

 mitotic figures. My preparations lead me to believe that the sublimate 

 effects violent mechanical injuries in delicate tissues. In such solid 

 tissues as the epidermis or intestinal epithelium there were no evidences 

 of injurious effects ; but among the very loosely aggregated masses of 

 cells that constitute some of the regenerated parts, there were signs of 

 serious damage. In the epidermis, for example, spindle figures occur 

 imbedded in a dense cytoplasmic mass. These figures were faithfully 



