AN OBSERVATION ON THE NUMBER OF BACTERIA IN DES MOINES 
SCHOOL BQILLINGS. 
BY L. S. ROSS. 
At the request of the President of the Polk County Medical Society 
in Novemher of last year, 1905, I made a little investigation into the 
bacteriological conditions of the school buildings of Des Moines. 
Because of circumstances the work was hurriedly undertaken and 
because of that fact, was more crudely done than it otherv\^ise would 
have been. Not having apparatus available for the determination of the 
number of bacteria in a measured quantity of air, and not having time to 
prepare such apparatus, it was necessary that the method adopted should 
be the rather crude one of exposing Petri dishes in the air of the school 
rooms for a definite period of time. It was also necessary that these 
dishes while being exposed, could not be under direct observation, con- 
sequently I do not know that in all instances they were all undisturherV 
although I believe such to have been the case. For these reasons, then, 
it will be readily understood that results obtained can be considered only 
as approximate instead of being scientifically accurate. For a period of 
thirty minutes a Petri dish containing ordinary gelatine medium was 
exposed in each building, in the room that was the most crowded with 
pupils. At the beginning of the exposure of the dishes in the rooms 
selected tor the purpose, the teachers gave the pupils a marching drill, 
or calisthenics — with one exception, that being in the case of the room 
in the West side high school in which the request was not made — in 
order that the dust of the room should be put into circulation. Teachers 
were requested to replace the covers on the dishes at the end of the al- 
lotted time and take them to the principal’s ofhee. 
Upon the return of the gelatine dishes to the laboratory they were 
placed in the incubator room and kept at room temperature for a period 
of forty-eight hours, with the exception of some of the dishes, which un- 
avoidably were permitted to stand sixty hours before the count of the 
colonies was taken. If the dishes' had been permitted to incubate longer, 
the probability is that a larger number of colonies world have develon- 
ed. As has already been stated, the determination of number per cubic 
meter could not be made by the method employed. The number oC 
colonies on the gelatine plates exposed in the different buildings is as 
follows : 
Benton, Room 1 I,!")© 
Bryant, Room 10, 
Curtis, Room 5, Oo.i 
Bremer, Room 1, ,^75 
Emerson, Room 5 1,.3*J0 
East ffigh Assembly Room, .Ss6 
East High Toilet, Girls, 47S 
Lucas, Room 4, 7S4 
Webster. Room 8 4:15 
Longfellow, Basement 
Longfellow, Room 1 415 
( 21 ) 
