Effect of Drying upon the Viability of Bacteria. 107 



77 (686) 



The effect of drying upon the viability of bacteria. 

 By 0. E. A. WINSLOW and F. ABRAMSON. 



[College of the City of New York.] 



The curve of viability, measuring the rate of decrease among 

 bacteria exposed to an unfavorable environment, has been deter- 

 mined for many conditions. Drying is known to cause a rapid 

 elimination, but no exact quantitative determinations have been 

 made. In the experiments here reported, colon bacilli were used. 

 One cubic centimeter of a 48-hour broth culture was mixed with 

 2 ^2 grams of sea sand spread out in an ordinary Petri dish. 

 Duplicate dishes prepared in this way were covered with porous 

 earthenware tops and kept for various periods of time from four 

 hours to ten days. At the end of each period nine cubic centi- 

 meters of sterile water were added to the sand in one of the dishes 

 and well mixed by careful agitation. Portions of this water were 

 then plated in duplicate on agar in the usual manner. 



The results of eight series of tests are shown in the table 

 below expressed in percentages of the original number of bacteria 

 present. The original numbers in different series varied from 

 4,150,000 to 117,300,000 per gram of sand, and the final number 

 remaining after ten days in Series II and III were 20,700 and 

 18,900 per gram, respectively. The average temperature and 

 humidity of the room in which the plates were kept is shown for 

 the last five series at the bottom of the table. 



Percentage of Original Number Surviving. 



Period. 



Series. 



Hours. 



I. 



II. 



III. 



IV. 



V. 



VI. 



VII. 



VIII. 



4 













76.45 







si 













57-18 







6 









75-90 







79.82 





7 











57-56 



37-46 





57.76 



8 









67.23 



59-30 





69-03 





10 











44.48 







41.38 



24 



.85 



•85 



•85 













48 



.16 



.16 



• IS 













120 



.08 



.06 



.06 













166 



.04 



.04 



.04 













216 





.02 



.02 













240 





.02 



.02 













Average temperature 





69 0 



69° 



70° 



69 0 



69 0 



Average relative humidity . . . 



90% 



72% 



60% 



90% 



72% 



