ON THE NATURE OF MITOCHONDRIA 205 
The chief methods employed in cytological studies are based on 
the reactions of stains and chemicals on protoplasm. In many 
cases a differentiation between cells and cell structures is demon- 
strated solely by staining reactions. While such methods may 
be criticized on account of the absence of a definitely indicated 
specificity, their value cannot be denied, especially in cases where 
the difference is pronounced. It is fair to demand when struc- 
tures bear so close a resemblance to each other as mitochondria 
do to bacteria that some method must be employed that will 
differentiate between the two if they are to be considered distinct 
structures. 
Cowdry (18 p. 72) says: ‘‘It occasionally happens that tissues 
prepared for mitochondria have been invaded by bacteria, in 
which case the bacteria stain just like the mitochondria by the 
Benda method, with iron hematoxylin and with fuchsin methyl 
green. I have found that large bacilli contain granules which 
stain intensely and apparently specifically with janus green. 
They resemble in distribution the so-called polar granules. 
Smaller forms often stain diffusely.’ It is not clear from this 
statement whether Cowdry means to limit this staining reac- 
tion of bacteria to those forms that have invaded cells or if he 
implies that bacterial smears fixed and stained by mitochondrial 
methods will give the same results. In another place, Cowdry 
(18, p. 135), referring to mitochondria, says: ‘Fortunately, 
they may be easily distinguished from bacteria by their staining 
reactions (particularly to janus green), by their occurrence in 
almost all cells, by their behavior and by their lack of independent 
motility.” 
This latter statement would appear to imply that all bacteria 
possess independent motility. This would be contrary to estab- 
lished fact in bacteriology. Just what ‘behavior’ of bacteria 
is specifically characteristic is not indicated by Cowdry. 
Concerning the staining reaction of bacteria to Janus green, I 
cannot agree with Cowdry that ‘‘mitochondria are easily dis- 
tinguished from bacteria’”’ by this staining method. 
The practically universal occurrence of mitochondria in plant 
and animal cells points to a fundamental property of these struc- 
