452 IVAN E. WALLIN 
removal from the previously killed animal, smears of the organs 
and tissues were made on microscopical slides. The smears 
were then permitted to dry in the air without any other fixation. 
A large number of bacterial staining methods were later applied 
to the smear preparations. Most of these staining methods have 
no selective action on bacteria, and consequently the entire smear 
was stained and mitochondria could not be distinguished with 
any important degree of clarity. In a few instances Gram’s 
stain appeared to give a little clearer differentiation. One bac- 
terial staining method was found, however, that gave a sharp 
differentiation—Pappenheim’s pyronin-methyl green. This stain 
has had very extensive use in bacteriological technique. ‘Todd 
(18) recommends it especially for the demonstration of bacteria 
in cells on account of its selective action. In this study saturated 
aqueous solutions of pyronin and methyl green have been used 
in various proportions of mixture. In some instances it was 
found that a special proportion of the two stains was necessary to 
produce sharp differentiation. As Todd has recommended for 
the demonstration of bacteria, it is necessary to experiment with 
the proportions of the two stains to attain the best results. 
RESULTS OF BACTERIOLOGICAL STAINING METHODS ON TISSUE 
SMEARS 
Figure 6 is a camera-lucida drawing of a part of a young 
rabbit pancreas smear after pyronin-methyl-green staining. 
There was only a small area in the entire smear that appeared 
like the illustration. It is only in a very few cases out of a 
great number of attempts that anything resembling mitochondria 
were present in pancreas preparations. The bodies in the 
smear, represented in figure 6, appear like mitochondria, but not 
like the typical mitochondria of pancreas cells. Obviously, I 
am not in a position to definitely state that these bodies are mito- 
chondria. It appears probable to the author that these bodies 
are the fragments of the original mitochondria of the pancreas 
cells. They may be artifacts. If they are, then, what evidence 
do we have of the reality of mitochondria in stained preparations? 
