A Sterile PutresoiUe Fluid. By W. H. Ballinger. 
289 
germs ; and more than this, judging by analogy it is extremely 
probable, from their necessary minuteness, that, presuming they 
exist, they are outside the limit of our present optical resources. It 
is therefore an actual gain to have presented to us, another method 
of determining the existence of particles, ultra-microscopic, as pre- 
cursors to the origin of bacteria in otherwise permanently sterile 
fluids ; because we may, at least by analogy, approximate to cer- 
tainty as to whether these particles, so exquisitely minute, are or 
are not organic germs. If their development be carefully studied, 
and if we can find other organized forms nearly related to the 
bacteria with known and demonstrable germs, and if we can diffuse 
these germs through the air, and expose suitable fluids to it under 
proper conditions, we shall have strong evidence in favour of, or 
adverse to, the highly probable presumption, that the particles 
demonstrated by Dr. Tyndall are germs. 
This idea became manifest to me immediately on studying 
Dr. Tyndall's facts. Now it is well known that the Monads or 
Heteromita are not far removed from the bacteria in structure; 
they are larger, and therefore more amenable to the optical re- 
sources at our disposal. During the past four or five years, by 
the joint labours of Dr. Drysdale and myself, it has been clearly 
shown that in six instances fully worked out the monads produce 
minute germs in enormous abundance. 
Now we have shown, at first by accident, that if the residuum of 
a maceration or infusion be allowed to dry up, it becomes a light, 
hard, porous, papier-mache-like mass ;* and if this be put again 
into a suitable fluiu, the peculiar monad, which the infusion, 
represented by the dried mass, contained, will reappear very speedily 
with great vigour. 
It struck me that this fact might be utilized in experiment ; and 
I proceeded to make some investigations, which yielded most in- 
teresting results, and which were briefly recorded in a paper in the 
' Popular Science Keview.' f 
We had proved that not only bacteria, but monads and even 
Stylonichia fustulata could live, flourish, and multiply in Cohn's 
nutritive fluid, % which contains no albuminous matter, but only 
mineral salts and tartarate of ammonia. If the ingredients are all 
mixed the fluid becomes speedily bacterious ; but if the tartarate of 
ammonia be kept by itself until required, and then be mixed with 
the salts, we have, with due precaution, an absolutely sterile but 
perfectly nutritive and putrescible fluid. 
Passing over the experiments detailed in the ' Popular Science 
Keview,' which my later tests have fully confirmed, the following 
two sets of facts appear to me to have considerable interest. 
* Vide ' M. M. J.' vol. xii. pp. 262-3. f April 1876, p. 121 
X ' M. M. J.' vol. xiii. p. 190. 
