[Vor. 1 
50 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
culosis in the inoculated animals resulted. In other experiments, 
guinea-pigs, instead of being inoculated, were directly exposed 
to the coughing of tubercular patients with the result that a 
number of the animals so exposed contracted tuberculosis. 
Varied and repeated experiments along these lines established 
the fact that in the acts of coughing, sneezing, and loud speak- 
ing, fine droplets of mucus are ejected into the air, that they 
float about and may be wafted by air currents, such as obtain 
in ordinary rooms, to a distance of from 24 to 40 feet. 
The most thorough investigation in recent years of the 
problem of air pollution with micro-organisms was made by 
Dr. М.Н. Gordon. This author believed that the positive 
recognition of disseminated saliva constituted an important 
step in the development of an applicable bacteriological method 
for the examination of air. By bacterial analyses of a number 
of samples of saliva obtained from normal individuals, Dr. 
Gordon determined that the streptococci are the organisms 
most abundantly present in saliva. Of these he was able to 
differentiate four morphologically different types—longus, me- 
dius, brevis, and conglomeratus. In endeavoring to differentiate 
these organisms on а physiological basis a study was made of 
their virulence, relation to oxygen, optimum growth temper- 
ature, pigment production, motility, gelatin liquefying power, 
indol production, action on litmus milk at 37°C., and action on 
various carbohydrates. 
It was found that the micro-organism which is most useful 
in the detection of droplets of saliva is Streptococcus brevis 
because it is the only one among the salivary cocci found which 
changes the color of neutral red broth to yellowish green, and 
produces acid and clot in milk. Having developed a means 
of differentiating the coccus most characteristic of saliva, Gordon 
next examined the open air for the presence of micro-organisms 
characteristic of saliva. In these experiments broth plates were 
exposed for a stated length of time and incubated anaérobically 
at 37°C. In but very few cases were the organisms isolated 
from the air. 
A further means of differentiating the characteristic salivary 
1 Loc. cit. 
