BACTERIA IN DIPHTHERIA. 377 



" Our experience lias been that the Bacillus diphtherias 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. Loffler 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 toxaemia 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 which 

 we give below. Subcutaneous inoculations in guinea-pigs of a small 

 quantity of a pure culture of the bacillus (0. 1 to 0. 5 cubic centime- 

 tre of a bouillon culture) cause death in from one to four or five 

 days. The usual changes observed at the autopsy are " an exten- 

 sive local oedema with more or less hypersemia and ecchymosis at 

 the site of inoculation, frequently swollen and reddened lymphatic 

 glands, increased serous fluid in the peritoneum, pleura, and pericar- 

 dium, enlarged and hsBmorrhagic suprarenal capsules, occasionally 



