460 IVAN E. WALLIN 
dendum’ to a former article (Wallin, ’22), namely, that fragility 
is a resultant of symbiosis. Further, their fragility refutes 
Regaud’s contention that no bacteria are known which exhibit 
the fragility of mitochondria. 
The apparent fragility of the senile forms of Bacillus radicicola 
has a bearing on the problem of growing mitochondria on artifi- 
cial culture media. It is apparent from the absence of these 
forms in bacteriological literature that they have not been cul- 
tivated. This failure to grow them on culture media may be 
caused by various factors. It may be possible that they require 
a special culture medium. It is more likely, however, that their 
fragility does not permit a transfer. A third possibility presents 
itself, namely, that they may have lost the power of reproduction. 
This latter possibility appears the least likely explanation. It 
it quite certain that if success is to attend attempts to grow 
mitochondria in artificial culture media, the fragility of mito- 
chondria, as well as the proper culture medium, must be taken into 
account. 
There is no reason to suppose that all mitochondria and sym- 
biotic bacteria develop and possess the same degree of fragility. 
To the contrary, I have presented evidence in the preceding 
section of this paper in support of the contention that mito- 
chondria vary in fragility. 
It is perhaps excusable at this time to digress into the realm 
of theory. The question naturally arises: Would a symbiotic 
bacterial interpretation of mitochondria be antagonistic to es- 
tablished factors in the theory of evolution? 
Osborne (717) has stated a clear and logical conception of 
evolution on the earth. His conception includes a chemical 
evolution preceding and leading up to the establishment of 
definite organisms. The first organisms in this conception were 
of a bacterial nature. These primordial bacteria or bacteria- 
like organisms were able to subsist on inorganic material. This 
conception of the first life is strengthened by the discoveries 
of Alfred Fischer (00) and other later investigators. Fischer 
discovered a strain of bacteria that apparently represent the per- 
sistence of these primordial organisms, the Nitroso monas. 
