INFLUENCE OF ATMOSPHERIC TEMPERATURE. 1^7 



It is seen from the table that, when sprayed into the air under 

 similar conditions, living: cholera vibrios disappear from the air 

 in about six minutes and living? prodigiosus bacilli in about twenty 

 minutes, whereas sarcina remains alive for more than three 

 hours. There is a striking similarity shown by these organisms 

 in their relative resistance to drying on glass slides and their 

 persistance in the air when contained within fine droplets of 

 saline solution. It would seem, therefore, that had plague bacilli 

 been sprayed under similar conditions, the living ones would 

 have disappeared from the air between six and twenty minutes 

 after spraying. 



This similarity in the behavior of the organisms on the slides 

 and in droplets strongly suggests that also in the latter instance 

 the disappearance of the living bacilli from the air is due to 

 death from drying. If this were true, then if we were able to 

 retard the evaporation of the water of the fine droplets, the living 

 bacteria should remain in the air for a longer time. The most 

 obvious method of retarding the evaporation of the fine droplets 

 is to spray them into an atmosphere saturated with moisture. 

 The following experiment was therefore carried out. 



EXPERIMENT NO. 3. 



The chemical hood used in the previous experiment was also employed 

 for this one, but sheets of dry blotting paper were tacked against the walls 

 and strips of cloth were tacked to the ceiling and allowed to hang down 

 to within about 60 centimeters of the floor of the hood. A suspension of 

 cholera vibrios in 0.5 per cent sodium chloride solution was sprayed into the 

 dry hood, and Petri dishes were exposed for periods of two minutes each at 

 intervals of three minutes until we could assume (from previous experi- 

 ments) that living cholera vibrios were no longer present in the air. The 

 entire interior of the hood was then thoroughly sprinkled with water and 

 the cloths and sheets of blotting paper were also made soaking wet. After 

 the wet hood had been kept tightly closed for some time, the same cholera 

 suspension was sprayed into it for the same length of time as before; this 

 time, however, the pump was placed in a tin vessel which was covered with 

 towels soaked in hot water, so that the air going into the hood with the 

 spray would contain more moisture. Plates were exposed as before for 

 one hour. Then water was again sprinkled over the interior of the hood 

 and a suspension of sarcina in 0.5 per cent sodium chloride solution was 

 sprayed and followed a minute later by the same suspension of cholera 

 that was used for the previous sprayings. Plates were exposed for three 

 and one-half hours. 



