1894.] MICROSCOPICAL JOURNAL. 107 



of 24 hours an abundant characteristic growtli of the 

 diphtheria bacilli had developed in the two control dishes 

 but no growth was visible in those treated witli the for- 

 malin spray nor did any growth subsequently occur 

 therein the plates being kept under observation for a 

 month. 



Next, plate cultures were made in the usual way by in- 

 troducing the bacilli into glycerine agar made liquid by 

 heat, pouring the melted medium thus inoculated into 

 Petri dishes, and allowing it to solidify before using the 

 spray. Two were now sprayed with a 1 per cent; two 

 with a 1 to 1,000 ; two with a 1 to 2,000 ; and two with a 

 1 to 10,000 solution of formic aldehyde and placed in the 

 incubator with two control plates. Characteristic colon- 

 ies developed in the usual time in the control plates. In 

 those sprayed with the 1 to 100 and 1 to 1,000 solution 

 no colonies developed. In one of those sprayed with 1 

 to 2,000 a single colony developed and was found upon 

 examination to be a mould fungus ; the other plate re- 

 mained sterile showing that while a 1 to 2,000 solution 

 of formic aldehyde was sufficient to sterilize a culture of 

 the diphtheria bacillus, it had no effect upon a mould fun- 

 gus, a spore of which had accidentally fallen upon the 

 agar in the preparation of the plate. In the two plates 

 sprayed with 1 to 10,000 solution, a large number of col- 

 onies developed of various shapes and colors showing 

 that bacteria from the air had been carried into the plates 

 with the spray, which was not strong enough to inhibit 

 their growth. 



Although the amount of liquid carried to the plates by 

 the spray was very small, yet I was not sure in the first 

 series of experiments whether the entire thickness of the 

 medium had been penetrated, or whether the formalin 

 reached the bottom by means of the needle tracks ; but 

 in the second series it was clearly evident that a quan- 

 tity of a solution so dilute as 1 to 2,000, scarcely suflicient 



