662 
J. F. WINCHESTER. 
body, there are certain parts of it into which bacteria do not 
enter, or entering, remain vital for a very short time only, for 
the body juices and tissues of normal animals are free from 
them, and their occurrence in these places may almost always 
be accepted as a sign of disease. 
Should the pabulum supplied to bacteria contain an excess 
of either alkali or acid, the growth of the organisms is inhib¬ 
ited. Most true bacteria grow best in a neutral or feebly alka¬ 
line medium. Light will usually attenuate the virulence of 
pathogenic bacteria. The presence of certain substances, espe¬ 
cially some of the mineral salts, in an otherwise perfectly suit¬ 
able medium, will prevent the development of bacteria, and 
when added to grown cultures of bacteria, will destroy them. 
Bacteria which produce diseases are known as pathogenic 
those which do not, as lion-pathogenic. Between the two 
groups there is no sharp line of separation, for true pathogens 
may be cultivated under such adverse conditions that their viru¬ 
lence will be entirely lost; while at times bacteria ordinarily 
harmless may be made toxic bv certain manipulations or by in¬ 
troducing them into animals in certain combinations. 
A microbe having effected its entrance into an animal mav 
grow with such rapidity as to completely block the blood or 
lymph channels, thus stopping the proper circulation, and dis¬ 
ease and death must result. More common than this is a local 
establishment of the organisms with a resulting inflammation 
due partly to the pressure of the foreign organisms and partly 
to their toxic metabolic products. The term pneumonia is a 
vague one, really comprehending a variety of inflammatory con¬ 
ditions of the lungs quite dissimilar in character. This being 
true, no one should be surprised to find that a single organism 
cannot be described as specific for all. 
The bacterium which can be demonstrated in at least 75 
per cent, of the cases of lobar pneumonia and which is now al¬ 
most universally accepted as the cause of the disease, and about 
whose specificity very few doubts can be raised, is the pneumo¬ 
coccus of Frankel and Weichselbaum. 
