SPECIAL FORMS OF CONJUNCTIVAL INFECTION 197 



other hand, with antitoxic serum was able to agglutinate both true diphtheria strains 

 and also pseudo forms. 



The experiments were not conclusive, for a concentrated solution of a serum of a 

 definite Bacterium is able to agglutinate Bacteria which are allied to it (e.g., typhoid 

 serum agglutinates B. coli, and the Gram-negative cocci interact). We can only use 

 highly diluted sera, therefore, for the differentiation of allied strains, and such dilu- 

 tion can only be made with sera of high valency. Schwoner was able to produce a 

 very active serum from horses by treating them first with dead and then with virulent 

 diphtheria bacilli. This serum agglutinated the true diphtheria bacilli in a dilution 

 of 1 in 10,000. In such a dilution pseudo-diphtheri bacilli did not agglutinate. 



With a serum of this type, the agglutinating power of which for true diphtheria 

 was 1 in 5,000, Tertsch tested thirty-two strains obtained from the conjunctiva 

 (twenty-three from normal, five from catarrh, and four from xerosis). As many 

 strains will of themselves settle down, the bouillon in which the organisms are 

 must be carefully shaken, the serum added, and then the action observed for forty- 

 eight hours. The organisms from two forty-eight-hour-old blood-serum cultures 

 are rubbed up with bouillon in a mortar, and shaken till the organisms are in 

 suspension ; equal parts of the fluid and a 1 in 5,000 dilution of the serum are 

 mixed. Six strains from the normal conjunctiva were agglutinated; all others 

 were not. These six strains were quite avirulent for animals, two of them alone 

 merely causing a local infiltration. Tertsch considered these six strains as true, 

 though avirulent, diphtheria organisms. Morphologically, they could not be dis- 

 tinguished from the others ; their growth on agar was similar to that of diphtheria. 

 Four of the strains which were agglutinable gave positive pole-staining with 

 Neisser's method, one of them a negative result, and the other a variable one ; 

 all the strains which did not agglutinate were negative. All the agglutinating 

 strains produced an acid reaction in bouillon ; the non- agglutinating did not. 

 Some of the latter increased the alkalinity ; others did not affect it. 



Bacilli also wei-e found which were not pathogenic, but still were able to produce 

 an acidity in bouillon. From this we must conclude either that acid formation 

 is not a constant point of differentiation between the true and the pseudo bacilli 

 (calling the avirulent strains ' pseudo '), or that those avirulent bacilli which develop 

 acidity are not pseudo-bacilli, but are true diphtheria bacilli which have become 

 avirulent. There are even strains which are avirulent, form acid, do not stain by 

 Neisser method, and do not agglutinate, and yet do produce a small amount of acid 

 (Lehmann and Neumann). The development of acidity and the agglutination tests 

 are, therefore, not absolute points of differentiation. 



A. Knapp (who agrees with Axenfeld in recognizing several varieties of these 

 non-pathogenic bacilli) compared the fermentative, or rather the acid-forming, 

 power of twenty-seven virulent diphtheria bacilli, ten xerose, and four pseudo- 

 diphtheria bacilli with respect to serum-water, to which had been added dextrose, 

 mannite, maltose, lactose, saccharose, and dextrine (1 per cent, of each His), 

 diphtheria and xerose ferment dextrose, mannite, and maltose in the same way, with 

 acid- formation and coagulation. On the other hand, diphtheria alone ferments 

 dextrine, xerose alone saccharose. Pseudo-diphtheria bacilli do not cause fermenta- 

 tion, and form no acid. 



The essential point in the whole question is toxic activity, as shown on the one 

 hand by the production of infection and on the other by the effect of the curative 

 serum. There is no doubt that virulence is no constant attribute of the bacteria, 

 for not only can it vary in intensity, but it can be lost and regained. The occurrence, 

 therefore, of avirulent diphtheria bacilli is obvious and well established. Loffler 

 is right in insisting, before an identity can be established, that the organisms in 

 question must be similarly capable of producing a specific characteristic toxin 



