150 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



Klcincnberg's 70% alcohol hacmatoxj'liu followed by eosin, and (2) for 

 osmic material, the iron haematoxylin as used by Heidenhain.^ 



Slides bearing sections of picro-sulpliuric material were placed in 

 the haematoxylin solution for three or four minutes only ; it was found 

 advisable in some cases to dilute the stain with an equal amount of 

 70% alcohol. The superfluous haematoxylin was removed with 70% 

 alcohol and then the slide was simply dipped into a jar containing 

 70% alcohol with a fevv drops of a sat. solution of eosin in 70% alcohol. 

 Cornifying tissues are stained by the eosin bright red, which stands out 

 in beautiful contrast with the light blue of other tissues. By this 

 method pigment cells and their granules are finely demonstrated. I 

 found, however, with material fixed in the })icrc)-sulphuric mixture a 

 slight tendency to shrinkage, which made it inferior to Hermann's fluid 

 for general histological purposes. 



Material fixed with Hermann's fluid for three hours only was blackened 

 superficially ; this was corrected by Weigcrt's decolorizer. The iron- 

 haematoxylin stain was used in the usual way. 



Feather germs were sectioned transversely, longitudinally, and 

 obliquely, and were mounted in Canada balsam. Glycerine was used in 

 most cases for mounting sections of dry feathers. 



Teased preparations were also found very instructive, material fixed 

 in Hermann's fluid being especially favorable for such treatment. For 

 this purpose a feather germ was first split longitudinally into strips and 

 the epidermal portions removed from the pulp. These strips, after be- 

 ing stained in toto in haematoxylin followed by eosin, were teased on 

 the slide in balsam or xylol. Fully cornified portions were unstained 

 by the haematoxylin and eosin, but they retained a light brown stain 

 from the fixing fluid. Elements in process of cornification took an eosin 

 stain, which was deepest in the more advanced stages, though not ap- 

 pearing in the completely cornified elements. Stages preceding cornifi- 

 cation took the haematoxylin, as did also nuclei in cornifying portions 

 of the feather. 



Dry feathers have also been studied in toto, and control observations 

 have been made on them to guard against the possibility of overlooking 

 a pigment that might be dissolved by the histological reagents used. 

 This matter will be brought up later in a cliscussion of the chemical 

 characteristics of feather pigments. 



Besides Sterna liirundo, feather germs from Passerina ciris Linn., 



1 Picrocarminate of lithium lias been used for difTcrentiating cornifying tissues, 

 but I have found it inferior to the stains mentioned above. 



