90 



MICHIGAN ACADEMY OF SCIENCE. 



THE INFLUENCE OF FORMALDEHYDE ON THE GROWTH OF 



CERTAIN BACTERIA IN MILK. 



(la , abstract.) 



BY ARTHUR J. HOOD. 



The purpose of this paper is to ascertain the per cent of formaldehyde 

 that must be present in milk in order to prevent the growth of the 

 lactic acid bacillus, and the typhoid bacillus. 



Tubes each containing ten cubic centimeters of fresh skim- 

 med milk were sterilized in the autoclave, and then treated 

 with dilutions of formaldehyde and subsequently some of these 

 tubes were inoculated with the above mentioned micro-organ- 

 isms. Eight series of tubes containing formaldehyde were pre- 

 pared, in which the dilutions were as follows: No. 1, 1:100; No. 

 1*, 1:500; No. 3, 1:1000; No. -1, 1:5000; No. 5, 1:8000; No. (>, 1:10000; No. 

 7, 1:25000; No. 8, 1:50000. With each set there were control tubes con- 

 taining no foi-maldehyde which were inoculated with the germs. After 

 the tubes had been inoculated plates were made from each tube at the 

 intervals indicated in the accompanying tables and the colonies developed 

 on these plates were counted. The following tables give the results 

 of this investigation: 



B. CoU Communis. 



Time after inocula- 

 tion. 



1:100 



Immediate . 



1st hour 



2nd hour. . . 



3rd hour 



Ist day 



2nd day. . . . 



3rd day 



6th day 



9th day 



6 

 18 

 1 

 

 

 

 

 

 



1:500 



4 

 2 

 19 

 20 

 1 

 

 

 

 



1 :1000 



360 



120 



14 



31 



50 



















1 :5000 



240 

 66 

 12 

 6 

 6 

 1 

 2 

 

 



1 :8000 



240 



360 



840 



5 



40 



6600 



42000 



124000 



281000 



