316 PROFESSOR LISTER ON THE GERM THEORY 
and the intervals between acts of micturition would afford time for the 
organisms to spread extensively inwards if it were a tube of indifferent 
matter; but I hoped, in accordance with the principle which I had had 
reason on other grounds to believe in, that the organisms would prove 
unable to develope in this putrescible material, however favourable a nidus 
for their growth. If this were really the case, instead of having the urine 
drawn off with a catheter, with special precautions, as was done by a 
surgeon at PasTEeur’s request, if the skin round the orifice of the urethra 
were treated with an efficient antiseptic, say with a solution of carbolic acid 
in forty parts of water, the urine might then be passed from the patient 
from whom it should be obtained, perfectly uncontaminated, though unboiled, 
free from any living organisms. Accordingly, on the 16th November 1871 I 
performed the following experiment :—Six wine-glasses were heated far above 
the temperature of boiling water by means of a spirit-lamp. I may here 
remark that in the rest of this communication, wherever I use the word 
“heated” (in quotation marks), I shall wish to be understood as meaning that 
the thing spoken of is not hot when used, but that it has been heated far above 
the boiling point of water, and then allowed to cool. Six glasses, then, were 
thus prepared, “heated” by means of a spirit-lamp. A glass plate large 
enough to cover them all, and overlap them considerably, was also similarly 
“heated.” Urine was then passed into these six glasses with the antiseptic 
precaution that I have mentioned. Two of the glasses, before being covered, 
received each a minim of water from the tap; and into a third a much smaller 
quantity of water was introduced. To the rest no water was added, but 
one was left exposed for twenty-four hours to the air of my study, while 
the other two were put at once under the cover of the glass plate. After 
the lapse of forty-eight hours, quite in accordance with Dr SANDERson’s state- 
ment, the two to which the drops of water had been added were turbid from 
the development of large and active bacteria; and the one which received a 
very minute quantity of water was similarly affected, though in a less degree, 
while the other glasses showed no change. But when twelve more hours had 
passed, the glass which had been exposed to the air, without the addition of 
any water, presented spots of opacity in the cloud of deposited “ mucus,” and 
on examining a portion of the cloud with the microscope, I found in the first 
field several bacteria in full activity. But the other two which had been 
covered by the glass plate from the first were perfectly clear. I should say that 
after twenty-four hours these glasses, instead of being covered with the glass 
plate, were put under a glass shade common to them all; an exceedingly rude 
method of experimenting, merely intended to obtain rough evidence of whether 
exposure to the air would or would not lead to the development of bacteria. 
Considering, therefore, how imperfect were the means of excluding dust, I was 
