[Vor. 1 
68 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
intotheflask. Тһе contents of the flask were thoroughly shaken 
and aliquot portions, as shown in table rx, were plated with 10 
ec. of +1 nutrient agar. In plating, the introduction of much 
sand was avoided in the following manner: The end of the pipette 
was held immediately above the bottom of the flask while the 
liquid was being drawn up to a point slightly above the gradua- 
tion mark. After a few seconds, enough of the sandy liquid was 
allowed to run back into the flask to leave the water just at the 
mark. During this short interim a large proportion of the sand 
settled in the tip of the pipette and was returned to the flask 
as the liquid was lowered to the mark. Blanks were plated 
several times during the course of the experiments, but no 
growth developed in any case. 
The plates were іп all cases incubated for 4 days at 37°C., 
after which the number of bacterial colonies present in each was 
determined. Finally, all, or а representative number, of the 
colonies were examined for the presence of coccus forms. (See 
table rx.) 
The coccus colonies developing on agar are, as a rule, very 
small and often grow in the deeper strata of the medium. This 
renders the transfer difficult especially when two are to be 
made from the same colony—one for the stained preparation 
and one for the agar slope to be used as a stock culture. The 
difficulty was partially obviated by subculturing (from all the 
colonies in certain selected plates) to agar slopes, and incubating 
the latter at 37°C. After several days an examination served 
to eliminate the bacilli and moulds, leaving only the coccus 
cultures which were later examined for the presence of the sali- 
vary forms. In this examination the three differential media 
described above were used. 
SOURCES OF SAMPLES 
As the investigation in hand seeks to discover a relation be- 
tween the presence of a characteristic salivary organism and the 
pollution of air, it was thought best to collect the samples of 
air under normal conditions, i.e., conditions which are met with 
in every-day life. 
Public conveyances, on account of their usually crowded condi- 
tion and frequently inefficient ventilation, suggested themselves 
