12 MICRO-ORGANISMS AND DISEASE. [CHAP. 



the mouth of the flask (Fig. 3), and this is allowed to stand 

 for one night. Next day the boiling is repeated for half an 

 hour or more in the same manner as before. If the meat has 

 been fresh and the vessels and cotton-wool have been sterile, 

 twice boiling is found sufficient to destroy every impurity. 

 But to make sure, the broth is placed in the incubator and kept 

 there for twenty-four hours at a temperature of 32 38 C., 

 and then boiled on the next day for half an hour in the usual 

 way. The supposition is made, that if by any chance after 

 twice boiling the broth it should contain unchanged spores 

 of bacilli the only organisms that will resist boiling, although 



FIG. 2. A BUNSEN BURNER, WITH 

 ROSE FOR BOILING FLUIDS IN 

 TEST TUBES. 



FIG 



3. A FLASK CONTAINING STERILE 

 STOCK FLUID. 



they do not resist boiling for more than half an hour the 

 spores would germinate into bacilli when kept for twenty-four 

 hours in the incubator at 32 38, and these would then be 

 killed by the third boiling. As a matter of fact I have not as 

 a rule found any contaminating germs survive the second 

 boiling. It is of course to be borne in mind that during the 

 first as well as second and subsequent boiling the cotton-wool 

 plug is not removed from the mouth of the flask, but is only 

 raised out half its length from the neck. The cotton- wool and 

 he cotton- wool cap and beaker are replaced immediately or 



