SPECIAL FORMS OF CONJUNCTIVAL INFECTION 195 



removed from the type of the Loffler's diphtheria bacillus that they can at once be 

 differentiated from it. 



These forms are often found in the mouth, the throat, and the nose. On the 

 conjunctiva they are not so common. 



On the conjunctiva another type of avirulent bacillus is much more commonly 

 found. It is very similar in appearance to the true diphtheria bacillus, many strains 

 being identical, though in secretion preparations and in young cultures short, 

 thick forms are more commonly seen. Cultures on blood-serum are more scanty 

 than those of the true diphtheria bacillus ; the individual colonies are often very 

 dry, and adhere so closely to the medium that they cannot be washed away com- 

 pletely. In other strains this is possible. Cultures from a hypersemic conjunctiva 

 are generally more vigorous than those from the normal conjunctiva. In cultures 

 from many normal conjunctivas the colonies only begin to appear after several days. 



On agar the colonies from the normal conjunctiva as a rule are scanty and dry. 

 Their margins are serrated ; like those of the true diphtheria bacilli, under a 

 magnification of 60 the colonies appear freely granular. They vary greatly in size : 

 many strains, when grown on agar, do not form colonies larger than the head of 

 a pin ; others are slightly larger. They never 

 approach the colonies of the Hofmann-Loffler 

 bacillus in size. This type of non-virulent 

 bacillus, with its scanty growth, presents 



^ 



FIG. 40. XEROSIS COLONIES. FIG. 41. HOFMANN-LOFFLER 



VARIETY. 

 Figs. 40 and 41 are of the same magnification. 



features which are quite the opposite of those of the Hofmann-Loffler organism. 

 Lehmann and Neumann and others have given it the name Bacillus xerosis, and 

 Heinersdorff recommends the name Bacillus vulgaris pseudo-dijriithericus con- 

 junctivce, because he found it the most common inhabitant in the conjunctiva. 

 Undoubtedly numerous strains of both types have been observed, which have retained 

 their peculiarities under varying conditions and after long cultivation, or, at most, 

 have lost them to a very slight extent. I once cultivated a series of thirty strains of 

 the Bacillus xerosis type for a long time without finding any appreciable change. 

 Such strains must at least be classed as a variety. 



As an illustration of these different peculiarities, colonies of the same age (five 

 days) and at the same magnification have been photographed : (a) from two strains of 

 poorly growing xerosis ; (b) from the Hofmann type. All three were obtained from 

 the conjunctiva. 



The growth in bouillon so far resembles that of the diphtheria bacillus in that the 

 bouillon usually remains clear, while small punctate deposits occur on the sides and 

 bottom of the tube ; these can be shaken up, but soon sink again. The most 

 sparsely growing strains grow less freely than the diphtheria bacillus. The reaction 

 of the B. xerosis generally is not acid. 



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