MEANS OF DEFENCE AGAINST MICROBES. 243 
already said that air filtered through a sufficiently thick 
layer of cotton wool becomes free from germs, Guérin 
covers that part of the body in which the wound is 
situated with several layers of cotton wool, carefully 
applied and confined by a cotton bandage. This 
dressing permits the access of air to a certain extent, 
but the air is filtered through the cotton wool, which 
arrests all microbes ; and this is proved by removing 
the dressing after the lapse of several days, when the 
wound will be found to be in a satisfactory state, and 
in process of healing. A certain amount of pus is 
produced, but much less than in the old-fashioned 
lint dressing, and this pus is not putrefied, since the 
germs which are the agents of putrefaction have 
been excluded. 
The English surgeon, Lister, has arrived at the 
same result by a more complicated process, which 
has, however, been generally adopted in France. His 
process is based on the use of carbolic acid as an 
antiseptic or destructive agent of microbes and germs. 
Whenever an operation is to be performed, the instru- 
ments, the surgeon’s hands, those of his assistants, 
and all the materials used for dressing, must be 
steeped in a sufficiently dilute solution of carbolic 
acid; throughout the operation the wound must be 
surrounded with a spray of the same solution, playing 
over the hands of the surgeon and over all he touches. 
The same solution and the same precautions are 
applicable to the treatment of all wounds, whatever 
