34 



THE POPULAR SCIENCE MONTHLY. 



been exposed to a heat of from 158 to 167, without being free from 

 germs ; for, if we afterward add a quantity of broth which has been 

 sterilized at 230, the mixture of the two liquids, which, separate, 

 would have continued perfectly limpid, will shortly swarm with ba- 

 cilli and other organisms. Cohn's liquid can not be fully deprived of 

 active germs till it has been boiled for four hours. If, continues M. 



^ 



O'gO 

 oOoo 





ff 



JX 



u 



',-.:.'\ ' ":^\ 



|r- j x <-:'.- 'ill' 



(0 1003 



Fig. 5. Bacillus of the Atmosphere magnified 1,000 diameters. 



Miquel, we add sewer-water that has been heated for several hours in 

 an hermetically sealed retort at 176 to Cohn's liquid which has been 

 sterilized at 230, and place the mixture in a hot bath, nothing will 

 appear in it even after a month. Apparently it is perfectly free from 

 living -germs. But if a few drops of it are placed in a broth, also 

 fully sterilized, the broth will in a day or two appear full of bacilli. 



We must, then, unless we would expose ourselves to grave errors, 

 distinguish between apparent and real sterilization. While beef -broth, 

 neutralized with potash and heated to 230, will remain sterile for an 

 indefinite time, it is a good plan with other compositions and for par- 

 ticular bacteria to attain a temperature as high as 302. 



Heat, unfortunately, modifies the composition of organic liquids, 



