ATMOSPHERE IN RELATION TO PUTREFACTION AND INFECTION. 
31 
case seen on the surface of the exposed liquid. These waxed daily larger, and finally 
formed a thick layer on the top of every column. The liquid changed from a pale 
sherry to a reddish-brown colour, some of the tubes being more deeply tinged than 
others. 
On the 27th of September I provided myself with a microscope having a magnifying- 
power of 1200 diameters. Under its scrutiny the turbidity of the liquid immediately 
resolved itself into swarms of Bacteria in active motion. Cohn correctly explains the 
turbidity. The index of refraction of the Bacterium being slightly different from that 
of the surrounding medium, a scattering of light is the consequence. This scattering, 
however, and the opalescence it produces, are practically independent of the motions of 
the Bacteria. 
Since the date here referred to the exposed liquid has been frequently examined, both 
with the eye and with the microscope. To the former it is thickly turbid, to the latter 
it is swarming with life. Its smell is putrid. All this time the 'protected tubes 
exhibit a liquid perfectly unchanged in appearance. For four months it has remained as 
transparent and of as rich a colour as the brightest Amontillado sherry. 
On the 1st of October another experiment similar in principle to that just described 
was begun. Fresh urine was employed, and a much smaller case. The capacity of 
the latter was 451 cubic inches ; and three test-tubes, instead of twelve, were passed 
air-tight through its bottom. Like those in the larger chamber they were filled by a 
pipette, and boiled for five minutes in a bath of brine. Beside them were placed three 
other tubes containing the same liquid treated in exactly the same way, but exposed 
to the common air. On the 5th all the exposed tubes were turbid, and found by 
microscopic examination to be swarming with Bacteria. The colour of the exposed 
liquid changed from a pale sherry colour to a brown orange. On the 25th the tubes 
were again examined, and found full of Bacteria. Two months subsequent to this 
latter date the infusion, diminished by evaporation, was found well charged with 
Bacterial life. 
While this process of putrefaction was going on outside , the tubes opening into the 
moteless air of the case remained perfectly clear. 
The chamber represented in fig. 2, and above described, was the first operated on, 
and the liquid is shown by the draughtsman as filling only a small portion of the test- 
tubes. This smallness of volume is in part due to evaporation. Test-tubes U2 inch 
wide and 9 inches long were, in all subsequent experiments, nearly filled with the 
infusions. Strong in the first instance, these were sometimes kept until slow evapora- 
tion through the open tubes at the top of the case had reduced them to one third or 
one fourth of their original volume. Each experiment, therefore, was, in reality, a 
series of experiments, extending over months, on infusions of different strengths, the 
concluding ones of the series attaining a very high degree of concentration. In 
fig. 2 the portion of the tubes within the case ought to be less than one half of 
what it is there shown to be. 
