250 THE DIPHTHERIA BACILLUS 



serum the colonies are small, whitish in colour and almost transparent, 

 slightly raised and circular. It is not pathogenic to laboratory animals. 

 Usually, though not always, the association of this organism with the 

 diphtheria bacillus is unimportant from the point of view of prognosis. 



(ii) Staphylococcus pyogenes. Staphylococci constitute a more serious 

 complication than the preceding : respiratory complications are frequent. 

 In a case in which the staphylococcus aureus was associated with the diphtheria 

 bacillus the author observed a considerable swelling of the neck during 

 convalescence. 



(iii) Streptococci. According to Martin a secondary infection with strepto- 

 cocci produces the most severe form of diphtheria ; broncho-pneumonia 

 frequently supervenes in cases where streptococci are found with the diphtheria 

 bacillus. 



Metin demonstrated by experiment upon guinea-pigs the unfavourable influence 

 of Staphylococci and streptococci upon the course of the infection : he found that 

 the diphtheria bacillus in such cases multiplied in the blood stream and in the internal 

 organs and was present in enormous numbers at the site of inoculation. 



(iv) Bacillus coli. -The colon bacillus is not infrequently found in the 

 mouths of healthy persons, and it is therefore to be expected that it should 

 be found in the false membranes in some cases of diphtheria. The multipli- 

 cation of this organism is a serious complication ; three cases recorded by 

 Blasi and Russo-Travalli terminated fatally. These observers grew the 

 diphtheria bacillus and the colon bacillus together and showed that the 

 toxicity of diphtheria cultures was increased considerably. 



(v) Other organisms. Association with the pneumococcus, with the 

 pneumobacillus of Friedlander, with the proteus vulgafis, Vincent's bacillus 

 fusiformis and the anaerobic organisms of the mouth (Chap. XXXIX.) has 

 also been recorded. 



SECTION II. MORPHOLOGY. 

 1. Microscopical appearance. 



The diphtheria bacillus is a highly pleormorphic organism ; it is non- 

 motile, and does not form spores. [In general terms it may be described as 

 a small, slender, straight or slightly curved, usually irregularly-staining rod 

 with rounded and sometimes swollen ends : curved bacilli with swollen ends, 

 resembling a gherkin in appearance, are very characteristic. In size it is sub- 

 ject to considerable variation.] 



Various attempts have been made to classify the different varieties of 

 diphtheria bacilli. Three varieties may be distinguished depending upon 

 the length of the organism, viz. 



(a) Short bacilli almost like cocci. They measure about 2/j. x 0'8/x and often 

 occur in pairs arranged parallel to one another (p. 254). 



(b) Bacilli of intermediate size, measuring 3-4/^t x O8/*. These bacilli are 

 arranged parallel to one another or are found in pairs end to end, the latter 

 often forming an acute angle like the letter V or a circumflex accent. 



(c) Long bacilli 4-5/x or more in length. In culture they are seen to be 

 interlaced and without definite arrangement, very like brushwood. These 

 bacilli generate the most potent samples of toxin (p. 257) and are usually 

 found in severe cases of diphtheria. On the other hand, the short bacilli 

 (group a) are as a rule almost avirulent (Martin). 



[Another basis of classification of diphtheria bacilli is that worked out by 

 Cobbett. This observer relied on the staining reactions alone and was thus 

 able to distinguish five groups of diphtheria bacilli in young serum cultures. 





