SPERMATOGENESIS OF ASCARIS 425 
we use. For example, osmic acid stains all cytoplasmic inclu- 
sions in the developing sperm cell black or gray-black, while 
iron hematoxylin stains them all dark blue or black. But it 
would be quite inaccurate to say on the evidence given by these 
stains that all these bodies are composed of fat, or that they are 
all made of chromatin. For if we use a counter stain with the 
iron hematoxylin, such as Bordeaux red, we find that certain 
of these bodies retain the blue-black color while others readily 
give it up and take the red. They must therefore be quite differ- 
ent in chemical nature. ; 
The physiological cytologist insists that the true chemical 
nature of no protoplasmic structure can be told by its reaction 
to a stain. Many workers in this field have shown that the 
staining reactions of such material are almost wholly determined 
by the ionic sign of the fixative used, and so give little or no 
‘information concerning the chemical nature of parts. This is 
true; yet when two structures always stain differently after a 
given fixative it is fair to conclude that they are unlike chemi- 
cally. But the converse of this statement is true only when we 
use a very selective stain. In the hope of finding a truly differ- 
ential stain, one which would show in this broad way a difference 
of chemical nature, I used in the present study combinations 
of the following fixatives and stains: Flemming’s strong solu- 
tion, without stain; Benda’s modification of this solution and 
his ‘krystal violet’ stain; Altmann’s fixative and his acid fuchsin 
stain, washed in picric alcohol. Besides these reciprocal stains 
suggested by the men who designed the fixatives, I used the 
Ehrlich-Biondi-Heidenhain preparation and iron hematoxylin- 
Bordeaux red as double stains, not only after these fixatives but 
also after Carnoy and Lebrun’s fluid, sublimate-acetic, zur Stras- 
sen’s, Tellysnickski’s, Zenker’s, Miiller’s, and Bouin’s fixatives. 
The unstained osmic preparations are of little value from the 
point of view of differentiation, no matter how carefully treated. 
Altmann’s acid-fuchsin-picric-alcohol method is somewhat better, 
but it does not differentiate clearly the refractive body and the 
mitochondria or ‘plastochondria’ (Meves) from chromatic struc- 
tures. But most of the acetic fixatives show good differentiation 
