EELATION OF PATHOGENIC TO SEPTIC BACTERIA. 13 



exposing them for several hours, generally repeated several 

 times, to a temperature varying between 140° to 150° C. To 

 use cotton wool disinfected by prolonged (for several days or 

 weeks) steeping in absolute alcohol, or concentrated carbolic 

 acid solution, is not absolutely reliable. Overheating the 

 cotton wool in an air chamber to the above temperature till 

 singed has proved invariably and absolutely safe for all culti- 

 vations ; I have had to my regret failures in my cultivations 

 which could be referred to cotton wool soaked in concentrated 

 carbolic acid solution even for months. The same is to be said 

 of the flasks and test-tubes used. No amount of cleanins', 

 even with strong acid, is to be relied on ; nothing but over- 

 heating gives reliance. I at first always used to heat the 

 vessel well all round over the open flame of a Fletcher's 

 burner almost till the glass becomes glowing, and soon after 

 when the glass is still hot, but not as to do more than just 

 singe the cotton wool, I place in its neck the cotton-wool plug, 

 this having previously been overheated in the air chamber. 

 But lately I have overheated the vessels in the air chamber 

 to about. 140° — 150° C. for several hours, several times re- 

 peated, having previously cleaned them with distilled water, 

 and dried them as far as possible ; and I have found this 

 perfectly sufficient to disinfect them thoroughly. It cannot be 

 too strongly insisted on with Koch that the flasks and test- 

 tubes, and especially the cotton wool used as plugs for the 

 vessels, should be thoroughly sterilised by overheating, for it is 

 as much and as often that cultivations become thereby con- 

 taminated as by the non-sterility of the nourishing fluids or 

 the accidental entrance of organisms from the air. 



The filtered nourishing fluid (pork broth) having been re- 

 ceived in a clean flask plugged, as above stated, with long and 

 clean cotton wool, is boiled for about ten to fifteen minutes. I 

 never fill the flask to more than half its volume with the broth, 

 in order to avoid the fluid rising too high during boiling, and thus 

 wetting the cotton-Avool plug. This, although not necessarily 

 fatal, owing to the sterillity of the cotton wool, nevertheless [ 

 always avoid in this and other cases, for the sake of cleanli- 



