g2 LABORATORY BACTERIOLOGY 
EXERCISE XXXVI 
THE BACTERIA OF THE MOUTH 
140. In studying cultures from the throats of diphtheritic 
individuals one encounters many variations in the species of 
bacteria other than those of diphtheria which are present. 
The same condition holds true with the microscopic exami- 
nation of sputum for the tubercle bacteria. The fact has been 
determined that the organism of lobar pneumonia is often 
found in the human saliva, and, furthermore, a bacterium not 
distinguishable from that of swine plague is present in the 
upper air passages of a large percentage of healthy animals. 
In order, however, to isolate these organisms, it is usually 
necessary to resort to rabbit inoculation. 
Much attention has been given to the study of the bacteria 
of the mouth, and it seems desirable that a few examinations 
should be made for the purpose of learning something definite 
concerning the variety of species which are normal inhabitants 
of, and which seem to be somewhat localized in, the oral cav- 
ity, and consequently which may be encountered in seeking 
for pathogenic forms. In addition to those forms which seem 
to be more or less localized on the mucosa of the mouth, there 
is usually present in the oral cavity a large and changing variety 
of bacteria which have been introduced with the food. 
141. Work for this exercise. Examine carefully and describe 
fully the cultures made from sputum at the last exercise. 
Make a hanging-drop preparation from one of each of the dif- 
ferent kinds of colonies and describe the appearance of the organ- 
ism. Note the name of the genus to which each colony belongs, 
together with the approximate number of colonies of each. 
Make one or more cover-glass preparations from the mouth 
and ‘stain with alkaline methylene blue. Note carefully the 
varieties of bacteria found. 
