288 
Transactions of the Royal Microscopical Society. 
III. — Experiments with a Sterile Putrescihle Fluid exposed alter- 
nately to an Optically Pure Atmosphere, and to one charged 
with known Organic Germs of extreme minuteness. By Kev. 
W. H. Dallinger, Y.P.K.M.S. 
(Read be/ore the Eoyal Microscopical Society, Novemher 1, 1876.) 
By a series of carefully-conducted and well-controlled experi- 
ments, Professor Tyndall has recently shown* that sterilized 
organic fluids which have been filtered, will remain sterile for an 
indefinite time while they are kept in an atmosphere optically pure. 
It is well known that a beam of strong sunlight, even in diffused 
daylight, clearly reveals its path in the air ; but if in darkness, the 
intense beam of the electric light be sent through the atmosphere 
in its ordinary condition, the path of the beam will be vividly 
revealed by the light-scattering, which is the result of its impinging 
upon the innumerable organic and inorganic particles of varying 
minuteness with which the air is charged. But if air be enclosed 
in a suitable chamber, freed from all currents, and left undisturbed, 
it is now well known that it will by the action of gravity, in time, 
deposit all its particles, even the most extremely minute ; and the 
air will be left in such a condition that if the electric beam be 
caused to pass through it, its path — from the absence of even the 
most excessively minute motes — will be quite invisible. An atmo- 
sphere in this condition has been called " optically pure." Professor 
Tyndall has shown that in an atmosphere in this condition, properly 
sterilized, but putrescihle fluids, remain sterile. If, however, the 
same fluids be put into contact with an atmosphere charged in the 
ordinary way with motes, they become " infallibly smitten " with 
putrescence. It thus appears that there is a direct relation between 
the condition of the air and the origin of the septic ori^anisms which 
arise in sterilized fluids. The presence of the motes is, by the 
evidence of these experiments, essential to the production of the 
putrefactive organisms. The inference which comes readily and 
naturally to the mind is, that the germs or spore, or the bacterial 
equivalents of these, must be amongst the motes or particles 
in the charged atmosphere, and that their deposition into suit- 
able fluids determines their development ; whilst the " optically 
pure " atmosphere being wholly devoid of them the fluids remain 
sterile. 
This inference is apparently irrefragable. Nevertheless there is 
no direct evidence, so far as the bacteria are concerned — which are 
the organisms specially now in question — that there are actual 
* ' Nature,' Jan. 27 and Feb. 3, 1876, pp. 252 and 268 ; and ' Philos. Trans.' 
vol. clxvi. part 1, 1876. 
