108 THE AMERICAN MONTHLY [Apr., 



to moisten the surface, did penetrate to the bottom of a 

 film of solid agar, thicker than the false membrane which 

 usually forms in the throat in cases of diphtheria. 



I next made several stick cultures in glycerine agar 

 and dropped upon the surface of each tube, except the 

 controls, 5 drops of a solution of formic aldehyde of the 

 following strengths, 1 to 100, 1 to 200, 1 to 500, 1 to 1,000, 

 1 to 2,000, 1 to 5,000, 1 to 10.000 and 1 to 20,000. At 

 the end of 48 hours the control tubes showed an abun- 

 dant growth both upon the surface and along the entire 

 needle track (1 inch or more). None of the tubes to which 

 the 1 to 1,000 or stronger solutions were added, (some of 

 which I have here for your examination), show any sur- 

 face growth and if any growth has occurred along the 

 needle track, it must have been soon arrested as even af- 

 ter several days it is impossible to say that any more 

 bacteria are to be seen along the line of inoculation than 

 were introduced by the needle in inoculating the tubes ; 

 and subcultures made therefrom remain sterile. Of the 

 two treated with the 1 to 2,000 solution, one developed 

 a mould fungus as in the case of the plates. Some of 

 those treated with the weaker solutions grew, but less 

 vigorously than the controls. 



Another series of experiments was conducted with 

 smear cultures the formalin not being introduced in this 

 case until the cultures had been allowed to develop for 

 from 24 to 48 hours. Sub-cultures made from these, 

 after allowing the stronger solutions to act upon them 

 for a few moments, remained sterile, but the weaker 

 solutions were not so effective as when introduced at the 

 moment of inoculation, a minutes exposure to the 1 to 

 1,000 solution not always being sufficient to sterilize the 

 deeper layers of the surface culture. 



Two or three drops of pure formalin applied to the 

 cotton plug so that only the vapor came in contact with 

 the culture was also found to be sufficient to sterilize both 



