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to the forms. They were the identical species of the maceration, 
with which I am as familiar as with a barn-door fowl. What, 
then, is the logic of these facts ? Dr. Tyndall proves that bac- 
teria only develope in sterilized infusions when the air around 
them is laden with motes of incalculable multitude and exquisite 
minuteness. Given the presence of these, and the development 
of bacteria is inevitable. The inference is that the motes are 
germs . The above experiments show, that in closely allied 
septic organisms, the germs of which have been demonstrated 
and their developments watched, if the dry debris of a mace- 
ration in which these forms are found be scattered in the air 
around a prepared fluid, and demonstrated by similar optical 
means, that the said organisms develope ; but if the minute 
dust from the debris be optically proved to be absent , none of 
the monad forms appear. Here we do not hypothecate a germ, 
but we know that it exists ; and its deportment in similar con- 
ditions is identical with that of the assumed bacterial germ. 
Do we need more irresistible evidence that the bacteria develope, 
not de novo , but from genetic products ? 
Evidently Dr. Bastian thinks we do. He tells us in effect 
that if Dr. Tyndall has not succeeded, others have, in seeing 
bacteria reappear in infusions that have been exposed to a 
boiling heat for five minutes. This is true ; but not to the ex- 
tent nor with the meaning Dr. Bastian claims. He furnishes a 
list in “ Nature ” * for example, of those who are supposed to 
have secured the results he insists on. But this list is, perhaps 
hastily, but in effect, most unjustly framed. It is not surpris- 
ing to see strong protests from the investigators concerned.! 
The citing of Roberts, for example, or Lankester and Pode, 
or Pasteur or Schwann, is simply a meaningless exercita- 
tion to all but the ignorant. Stripped of all disguise, the 
number of cases of the appearance of bacteria in sealed infusion 
after five or ten minutes boiling is few and doubtful indeed. 
But still there are cases, and in one instance at least admirably 
attested ; but they are confessedly exceptional in a high degree. 
Dr. Bastian, however, prefers to interpret nature from the excep- 
tional flasks, and infer “ spontaneous generation ” rather than 
be guided by the cumulative and overwhelming evidence of the 
existence of bacterial germs, as the medium of their normal 
reproduction. This must mean either that he believes that 
these organisms originate de novo as well as by germs, which 
is a direct petitio principii ; or else that he is incapable of 
seeing the force of the facts which render the existence of 
germs inevitable. From the conflicting evidence of his own 
writing it would almost appear that he endeavoured to maintain 
Feb. 10, 1870. 
t E. G., “ Nature,” Feb. 24, 1876, p. 324. 
