196 SCIENCE PROGRESS. 



The morphological interest of the microbe lies in its 

 polymorphic character which is exceedingly well marked 

 in cultures upon eggs, and in the production of involution 

 forms. A spore formation does not exist. The distri- 

 bution of the bacillus is of considerable importance. It has 

 been found in the secretions of the throat of children free 

 from diphtheria as late as the twenty-fourth or thirty-first 

 day after disappearance of the disease (9) ; that this was 

 undoubtedly the specific bacillus was proved by cultivation 

 and by inoculation experiments. Sixty-five days after all 

 throat symptoms have vanished virulent bacilli capable of 

 establishing diphtheria in guinea pigs have been shown to 

 exist in the secretions of the nose (10). The demonstration 

 of pathogenic bacteria outside the body in water, air, or 

 upon articles of clothing, is a matter of great difficulty 

 since form and staining behaviour are insufficient criteria, 

 and in order to establish an absolute proof any suspected 

 pathogenic germ must exhibit its specific action upon a 

 susceptible organism. A proof of this nature has been 

 given for Bacillus diphtheria? by Park (11) and Abel (12). 

 The former detected the microbe in the dirty linen of a 

 patient suffering from the disease, the latter on a child's 

 toy. Wright and Emerson (13) have also furnished absolute 

 evidence that virulent bacilli can be recovered from the 

 sweepings of the floor of a diphtheria ward and from the 

 shoes of the attendants. The biological behaviour of 

 Bacillus diphtherial outside the body has been exhaustively 

 studied by Fliigge (14), who has pointed out that the 

 microbes will preserve their vitality as long as nine months. 

 The bacilli if dried or exposed to sunlight die rapidly, and 

 therefore currents of air cannot be a vehicle for the trans- 

 mission of the disease. 



The physiological behaviour of sub-cultures of the Klebs- 

 Loffler bacillus upon agar is shown by a diminution in 

 virulence, while an augmentation of this occurs in old 

 bouillon cultures. Escherich (15) considers that the rapid 

 production of acid when the bacillus is grown upon sugar 

 bouillon tinged with litmus is evidence of virulence. When 

 cultivated upon a medium containing peptone, Bacillus 



