332 DIPHTHERIA. 



brane (in the manner described below) and stained with 

 methylene-blue, the bacilli are found to have the following 

 characters. They are slender rods, straight or slightly 

 curved, and usually about 3 /x in length, their thickness 

 being a little greater than that of the tubercle bacillus. 

 The size, however, varies somewhat in different cases, and 

 for this reason varieties have been distinguished as small 

 and large, and even of intermediate size. It is sufficient to 

 mention here that in some cases most are about 3 /x 

 in length, whilst in others they may measure fully 5 /A. 

 Corresponding differences in size are found in cultures. 

 They stain deeply with the blue, sometimes being uniformly 

 coloured, but often showing, in their substance, little 

 granules more darkly stained, so that a dotted or beaded 

 appearance is presented. Sometimes the ends are swollen 

 and more darkly stained than the rest ; often, however, they 

 are rather tapered off (Fig. 81). In some cases the terminal 

 swelling is very marked, so as to amount to clubbing, and 

 with some specimens of methylene-blue these swellings and 

 granules stain of a violet tint. Distinct clubbing, however, 

 is much rarer than in cultures. There is a want of 

 uniformity in the appearance of the bacilli when compared 

 side by side. They usually lie irregularly scattered or in 

 clusters, the individual bacilli being disposed in all direc- 

 tions. Some may be contained within leucocytes. They 

 do not form chains, but occasionally forms longer than 

 those mentioned may be found, and these specially occur 

 in the spaces between the fibrin as seen in sections. 



Distribution of the Bacilli, The diphtheria bacilli may 

 be found in the membrane wherever it is formed, and may 

 also occur in the secretions of the pharynx and larynx in 

 the disease. It may be mentioned that distinctions formerly 

 drawn between true diphtheria and non- diphtheritic con- 

 ditions from the appearance and site of the membrane, 

 have no scientific value, the only true criterion being the 

 presence of the diphtheria bacilli. The occurrence of a 

 membranous formation produced by streptococci has already 

 been mentioned (p. 159). 



