194 



BACTERIOLOGY OF THE EYE 



nearly related to the true diphtheria bacilli, and often cannot be distinguished from 

 them, only they have no toxic power. These organisms have given rise to the 

 term ' pseudo-diphtheria bacilli.' 



The type which was first described under this name by Hofmann and Loffler, and 

 for which we now generally reserve the title ' pseudo-diphtheria bacillus,' is a Gram- 

 positive bacillus, which grows somewhat thicker and shorter on serum, and has very 

 slight tendency to the formation of club-shaped bodies or to segmental staining. 

 The rods tend to lie parallel to each other. On blood-serum, and still more on 

 agar, it grows much more vigorously than the diphtheria bacillus. 



Growth rapidly spreads over the surface of the media in the form of a thick 

 greyish-white scum. Later the agar often becomes brown. Growth is more 

 vigorous on potatoes, where a dry, uneven scum forms. A dense diffuse opacity 

 develops in bouillon, and in a few days a deposit, much more profuse and thick than 



FIG. 39. VARIATIONS IN SHAPE AND FORM or THE BACILLUS XEROSIS IN 



CULTURE. 



l-t>. Stained with Loffler's methylene blue; 7-9, M. Neisser's granular staining of blood- 

 serum cultures nine to sixteen hours old ; 7, virulent diphtheria bacilli (typical 

 granular staining) ; 8, xerose bacilli quite unstained ; 9, xerose bacilli imperfectly 

 stained (Heinersdorff). 



that formed by the diphtheria bacillus. In ordinary bouillon there is either no acid 

 formed, or else so little that the reaction remains alkaline as a rule ; on the 

 second day the alkalinity increases (with the diphtheria bacillus the media become 

 strongly acid). In sugar bouillon the acid formation is much less. On gelatine 

 at 18 C. free growth takes place without liquefaction. Neisser's granules either do 

 not stain at all in blood- serum cultures of nine to twenty hours, or do not do so in a 

 typical manner. 



This bacillus is quite avirulent for guinea-pigs. (Hawlett and Knight claim to 

 have transformed this organism, by passage through animals, into virulent diph- 

 theria bacilli, and also report that, by careful warming, they have produced the 

 Hofmann- Lomer bacillus out of the virulent diphtheria bacillus. Unfortunately, 

 they did not test whether diphtheria antitoxin influenced the action of the organisms 

 after they had become virulent.) 



As a matter of fact, bacilli showing the characteristics just mentioned are so far 



