4 
SPERMATOGENESIS OF NORMAL 
promising one. The observations here recorded on hybrids 
are only the beginning of a number which I hope to make. 
To Professor C. O. Whitman I am indebted for much en¬ 
couragement throughout the progress of my investigations. 
Had it not been for his generosity in supplying me with mate¬ 
rial, I could not have undertaken a study of hybrid pigeons at 
the present time. My thanks are also due to Doctor S. Watasc 
for many valuable suggestions regarding methods. 
METHODS. 
A number of different methods of fixing and staining were 
tried. Only the more important are mentioned. 
Flemming’s strong solution was, taking all in all, perhaps 
the most satisfactory killing reagent. Nothing was found 
superior to it for faithful preservation of the cell, as a whole. 
It reveals the cytoplasmic structure better than other reagents, 
and at the same time brings out the chromosomes distinctly. 
Excellent results were obtained when it was followed by an 
aqueous solution of saffranin for twenty-four hours, and this 
by a counter-stain of lichtgriin in 95% alcohol. Immersion in 
the green for only an instant is required; if left for too long a 
time the saffranin is completely obscured. After using the 
green, the preparation must be washed rapidly in absolute 
alcohol, and plunged into clove oil. It may then be mounted 
in balsam either direct from the clove oil, or first transferred to 
xylol or cedar oil. Such a preparation shows the supporting or 
Sertoli cells to the best advantage, perhaps. The fatty globules 
present in them are not brought out so well by reagents which 
do not contain osmic acid. The green stain also brings the 
sphere substance very distinctly into view. Flemming followed 
by Heidenhain’s iron-haematoxylin method also gave good 
results. 
Another killing fluid of almost equal value with the Flem¬ 
ming, is Hermann’s Platino-aceto-osmic mixture. It is ex¬ 
cellent when followed by a low per cent of alcoholic saffranin 
for 24 to 48 hours. After washing, the, preparation is decolor¬ 
ized with acid alcohol and then treated with gentian violet, ac ¬ 
cording to any of the well known methods. In the final clear¬ 
ing clove oil is used for a minute or two, and the preparation is 
