knew that
he had to reckon with germs in the wound itself, if the skin was broken,
with germs on the hands and instruments of the operator, and with germs
on the dust in the air. He must find some defensive power which was able
to kill the germs, at least in the first two instances, without
exercising an irritating effect on the tissues and weakening their
vitality. The relative importance of these various factors in the
problem only time and experience could tell him. Carbolic acid had been
discovered in 1834 and had already been tried by surgeons with varying
results. At Carlisle it had been used by the town authorities to cope
with the foul odour of sewage, and Lister visited the town to study its
operation. In its cruder form carbolic proved only too liable to
irritate a wound and was difficult to dissolve in water. Lister tried
solutions of different strengths, and finally arrived at a form of
carbolic acid which proved to be soluble in oil and to have the
'antiseptic' force which he desired--that is, to check the process of
sepsis or putrefaction inside the wound. He also set himself to devise
some 'protective' which would enable Nature to do her healing work
without further interference from without. Animals have the power to
form quickly a natural scab over a wound, which is impermeable and at
the same time elastic. The human skin, after a slight wound, in a pure
atmosphere, may heal quickly; but a serious wound may continue open for
a long time, discharging 'pus' at intervals, while decomposition is
slowly lowering the vitality of the patient. Lister made numerous
experiments with layers of chalk and carbolic oil, with a combination of
shellac and gutta-percha, with everything of which he could think, to
imitate the work of nature. His inexhaustible patience stood him in good
stead in all these practical details. Rivals might speak contemptuously
of the 'carbolic treatment' and the 'putty method' as if he were the
vender of a new quack medicine; but at the back of these details was a
scientific principle, firmly grasped by one man, while all others were
groping in the dark.

[Illustration: LORD LISTER

From a photograph by Messrs. Barraud]

During 1866 and 1867 we see from his letters how he set himself to apply
the new principle first to cases of compound fracture and then to
abscesses, how closely and anxiously he watched the progress of his
patients, and how slow he was to claim a victory before his confi