BACTERIA IN DIPHTHERIA. 455 
‘‘ Our experience has been that the Bacillus diphtherize grows on ordinary 
steamed potato without any preliminary treatment, but that the growth is 
usually entirely invisible or is indicated by a dry, thin glaze after several 
days. Doubtless the invisible character of the growth has led most observers 
into the error of supposing that no growth existed, whereas the microscopi- 
cal examination reveals a tolerably abundant growth, which on the first po- 
tato is often feebler than on succeeding ones. Irregular forms are par- 
ticularly numerous in potato cultures, and in general the rods are thicker 
than on other media. In twenty-four hours, at a temperature of 35° C., 
microscopical examination shows distinct growth. We have cultivated the 
bacillus for many generations on potato.” 
Milk is a favorable medium for the growth of this bacillus, and, 
as it grows at a comparatively low temperature (20° C.), it is evi- 
dent that this fluid may become a medium for conveying the bacillus 
from an infected source to the throats of previously healthy children. 
Cultures of the diphtheria bacillus may retain their vitality for 
several months, and when dried upon silk threads for several weeks 
colonies are still developed in a suitable medium—in the room from 
three to four weeks, in an exsiccator five to ten, and in one instance 
fourteen weeks. In dried diphtheritic membrane, preserved in small 
fragments, the bacillus retained its vitality for nine weeks, and in 
larger fragments for twelve to fourteen weeks. 
The thermal death-point, as determined by Welch and Abbott, is 
58° C., the time of exposure being ten minutes. Léffler had previ- 
ously found that it did not survive exposure for half an hour to 60° 
C. With reference to the action of germicidal and antiseptic agents, 
we refer to the sections in Part Second relating to this subject. 
Pathogenesis.—In view of the evidence heretofore recorded, it 
may be considered as demonstrated that this bacillus gives rise to 
the morbid phenomena which characterize the fatal disease in man 
known as diphtheria. 
We have already referred to the effects of inoculations into the 
trachea in rabbits and cats, which give rise to a characteristic diph- 
theritic inflammation, with general toxeemia and death from the 
absorption of soluble toxic products formed at the seat of local in- 
fection. This inference as to the cause of death seems justified by 
the fact that the pathogenic bacillus does not invade the blood and 
tissues, and is supported by additional experimental evidence (see 
pages 309-317). 
PSEUDO-DIPHTHERITIC BACILLUS. 
Léffler, Von Hoffmann, and others have reported finding bacilli 
which closely resemble the Bacillus diphtheriae, but which differ 
from it chiefly in being non-pathogenic. The following account we 
