BACILLUS DIPHTHERIA. 285 



the latter. It is not uncommon to find one end, and 

 often even both, swollen; here and there there are 

 distinct cluh-like forms. In an un- 

 stained condition the pole, and often 

 also other portions of the bacilli, 

 present a highly refracting appear- 

 ance. When stained with methylene 7o TV ^v. * 



J Fig. 82. Diphtheritic 



blue these portions of the rods take bacilli x 1200. 

 on the stain markedly, and thus there > ^VSk a ^ h 

 is not uncommonly an appearance as J > involution forms. 

 if the bacillus were composed of short pieces with ir- 

 regular outlines. In the case of some bacilli, more 

 especially when they are taken from cultivations on 

 soil which was not very favourable for their growth, 

 the ends appear very markedly enlarged, or the middle 

 is distinctly thickened, or the rod is divided into large 

 roundish or oval bodies. These deviations from the 

 normal form of the bacilli, the club-like swellings, and 

 the fragments which arise by fission, evidently imply 

 the occurrence of involution. In favour of this view we 

 have the fact that when they are grown on the best 

 soil in the living body these abnormal swellings 

 seldom appear, and are much less marked, so that there 

 is only a slight thickening of individual portions, and 

 more especially of the ends. On the other hand these 

 appearances are the more numerous the worse the soil, 

 and the more imperfect and slow the growth. We 

 might be inclined to look on the portions of the bacilli 

 which are highly refracting as spores, or at least as the 

 commencement of the formation of spores, but Loeffler 

 was able to show that the rods, even when they showed 

 large numbers of these bodies, died without exception 

 after being exposed for half an hour to the temperature 

 of 60 C. Nor is there any better reason for looking on 

 these bodies as the early stage of arthrospores at any 

 rate not till we have some evidence that they possess a 

 greater resisting power to noxious influences than 

 bacilli in which this change has not occurred. At the 

 temperature of the room .the cultivations retain their 

 vitality for about three months. 



