INFLUENCE OF ATMOSPHERIC TEMPERATURE. 1^5 



This experiment was done in a hirge room with the doors and 

 windows closed. The bacteria upon the slides were exposed to 

 diffuse daylight during the first few minutes and were then 

 placed in a covered box. The temperature of the room ranged 

 between 32°. 5 and 33". 6 Centigrade and the dry-bulb thermom- 

 eter registered about five degrees lower than the wet-bulb one. 



This experiment indicates, as do several other similar ones 

 that we have done, that the plague bacillus occupies an inter- 

 mediate position between cholera and prodigiosus with regard 

 to its resistance to death from drying. Sarcina is much more 

 resistant than the other organisms. 



Having determined the relative resistance to death by drying 

 of sarcina, B. prodigiosus, and cholera vibrio when spread in a 

 thin layer upon glass slides, we next planned an experiment to 

 find the result with these same organisms when contained in fine 

 droplets of saline solution suspended in the air. 



EXPERIMENT NO. 2. 



Fresh cultures of the bacteria were suspended in 0.5 per cent sodium 

 chloride solution, the cholera suspension being made thicker than the 

 prodigiosus and the latter thicker than the sarcina.° The spraying was 

 done by means of an ordinary throat atomizer connected by rubber tub- 

 ing with a double cylinder force-pump such as is used for filling automobile 

 tires. The spray was directed during a period of half a minute toward 

 all parts of a chemical hood, measuring 175 centimeters long, 80 centi- 

 meters deep, and about 2 meters high. Paper had been previously pasted 

 over all cracks in the hood, and arrangements had been made for sliding 

 a Petri dish into the hood over moist blotting paper by opening a small 

 orifice for only two or three seconds. 



The cholera suspension was sprayed first and plates^ were exposed in the 

 hood at intervals until we judged (from preliminary experiments) that 

 all the living cholera vibrios had disappeared from the air. The hood 

 was then thrown open and about fifteen minutes later a similar experiment 

 was performed with the prodigiosus suspension. Then the hood was again 

 left open for a while and finally the experiment with sarcina was done. 

 Each Petri dish containing solidified agar-culture-medium was left in the 

 hood for a period of two minutes. 



' The prodigiosus suspension was shown by plating out in agar to con- 

 tain 120,000,000 organisms per cubic centimeter, the sarcina suspension, 

 33,000,000; the number per cubic centimeter in the cholera suspension was 

 not determined. 



