DIPHTHERIA 151 



with Streptococci, and in some few cases of apparently indisputable diph- 

 theria it has seemingly been wanting. It is a true parasite, and in cultures 

 requires the very best nutriment. Growing best upon blood-serum, to which 

 has been added bouillon and sugar, it shows a tendency even on this medium 

 to produce involution forms, although it multiplies rapidly. Irregularly 

 swollen rods arise, and even cells with short branchings (Fig. 37). As was 

 already mentioned, these have been without sufficient reason looked upon as 

 representing a higher morphological stage than the normal rods. 



In the diphtheritic membrane, and in fresh cultures, the bacillus appears 

 as a minute, somewhat clubbed or oval, rod-like cell about 1-5-2 fj. long 

 by 0-5 // thick. It is non-motile, and spores are unknown. In young 

 cultures the cell-contents stain apparently uniformly. Not infrequently 

 strongly-tinged granules can be seen, and these when they are large and lie 

 at the ends of the cell give the impression of spores. They are, however, 

 nothing but ' chromatin ' granules, such as have been already described. 

 The apparently uniformly-stained cell-contents have the same structure 



colt; k t Vibrio cholerae, single cells and chains. Magn. about 1500 



as in other bacteria, the protoplasm surrounding a sap cavity which, as in 

 all elongated forms, is divided into chambers by transverse walls of plasma. 

 In old cultures the protoplasm diminishes in quantity, and the septa 

 retreat from one another, so that the stained rods then appear transversely 

 striped (Fig. 28, /), broad, colourless stripes alternating with coloured plasma 

 streaks. The actual structure of the cell does not change, but becomes 

 more visible by reason of the changes mentioned. 



The diphtheria bacillus is not found in nature, and as yet has been detected 

 in a living condition only in situations where its derivation from human 

 patients was certain on soiled linen, floors and walls of rooms, children's 

 toys, and the mouth and nasal cavity of those attending diphtheria cases. 

 The dry cells remain infectious for many weeks. 



