ORGANISMS WHICH PRODUCE DISEASE 67 



practically the only pathogenic member the others being 

 usually termed pseudo-diphtheria, diphtheroid, or diphtheria- 

 like bacilli. From these it can be distinguished by various more 

 or less refined staining and cultural methods, and also by in- 

 oculation into animals. Infection may be communicated directly 

 from infected persons, or from animals such as the cat, or may 

 be carried by articles contaminated by sputum and secretions, 

 e.g. milk, dust of rooms, bedding and clothes, dishes, etc. The 

 inhalation of cough-infected air is one of the most usual means 

 of contracting the disease, which has naturally become more 

 prevalent since the introduction of compulsory education. 

 The site of infection is usually the throat and neighbouring 

 parts, and it is specially dangerous when it spreads to the 

 larynx. The nose, eyes, occasionally the genitals, and some- 

 times the skin, especially if already injured, may be affected. 

 The bacillus, as explained in a previous chapter (p. 56), re- 

 mains more or less localised in the lesion, whilst the toxins 

 which it manufactures pass into and circulate throughout the 

 body, sometimes causing serious damage to the heart, kidneys, 

 nervous system, vessels and other tissues. 



The typical local lesion, often well seen on the tonsil, is a 

 dirty yellow patch of ulceration covered with a " false mem- 

 brane" resembling wash-leather in colour and appearance, 

 and due to necrosis (i.e. death) of the mucous membrane 

 and other changes. This typical appearance is not always 

 seen. The part affected may be out of sight, or it may be 

 atypical perhaps merely a reddening and swellingof the throat. 

 Such cases can be diagnosed only by bacteriological methods, 

 and this is also true of the " carrier-cases " already discussed 

 on p. 55. Other organisms such as Pneumococci, Streptococci, 

 M. catarrhalis, Staphylococci, Diphtheroid Bacilli, are usually 

 found along with the Diphtheria Bacillus in increased numbers. 



The bacillus varies greatly in size, small, medium .and large 

 forms being recognised. It is non-motile and Gram-negative. 

 It is best examined when grown in a young serum culture, on 

 which medium it grows very rapidly, outstripping most other 

 organisms. Microscopic examination of such a culture usually 

 shows a peculiar grouping of the bacilli, due to the method of 

 division, and suggesting groups of spilt matches, or, as some 

 of the books describe it, like Chinese letters. With special 

 staining-methods, peculiar granule-like bodies may be demon- 

 strated, which are of considerable importance as aids to the 

 diagnosis (see Frontispiece, fig. 10). In doubtful cases, certain 

 differential cultural tests, and the inoculation of a guinea-pig, 

 usually with a small quantity of a broth culture which will also 

 contain the free toxin manufactured by the bacilli, are neces- 



