MEANS OF DEFENCE AGAINST MICROBES. 243 



already said that air filtered through a sufficiently thick 

 layer of cotton wool becomes free from germs. Guerin 

 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, arid 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 



