MTIOLOGY 



1845 



disease until the vitality of the host is lowered by some agency, 

 such as a chill, an attack of diarrhoea, or some intercurrent disorder, 

 when they are capable of producing their ill-effects. 



This carrier problem in the aetiology of dysentery is of great 

 importance, and though as yet it has never been conclusively proved 

 that an outbreak has been due to a carrier, still it is known that the 

 bacilli can be excreted in an intermittent manner by people suffering 

 from mild relapses. The dysentery carriers are classified into — 

 (i) healthy, (2) precocious, (3) convalescent, (4) relapsing, and 

 (5) chronic carriers. The healthy carrier is rare, but May has 

 found 22 out of 573 persons examined during an epidemic. The 

 precocious are believed to be very rare. The convalescent and re- 

 lapsing carriers are well known, of which the latter are of the greatest 

 importance in spreading the disease. The chronic carrier excretes 

 but few bacilli, but may be of importance in the spread of the disease. 

 With regard to the geographical distribution of the principal forms 

 of bacilli, it maybe stated that practically all of them seem to have 

 a cosmopolitan distribution. 



^Etiological Classification of Bacterial Dysenteries. — ^An aetiological 

 classification of bacterial dysenteries has been suggested as follows : — 



L Due to B. dysentericB Shiga-Kruse — Bacterial dysentery 

 sensU stricto. 



IL Due to mannite fermenting dysentery bacilli (Flexner, 



Hiss and Russell, Strong) — Paradysentery. 

 IIL Due to germs having the general character of the dysentery 

 bacilli ; but slowly fermenting (acidity only) lactose and 

 not agglutinated by Shiga-Kruse, and paradysenteric 

 serums — Metadysentery. 



Pathology. — The bacilli taken into the body with food and drink 

 pass to the intestine, in which they grow and multiply, and along 

 the whole length of which they can be found. The researches of 

 Flexner and Sweet have proved that the bacilli can abound in the 

 small intestine, where no pathological lesion may be found. In 

 the bowel they give rise to the toxins, of which two are known — 

 one which acts upon the lower bowel, and the other on the nervous 

 system. Both these toxins are absorbed into the blood, but the 

 first, being excreted by the large bowel, causes the lesions well 

 known to be associated with dysentery, and explains the locahza- 

 tion of these lesions. In the process of excretion this toxin first 

 causes an exudation of lymph into the submucosa, and later into 

 the mucosa. This lymph coagulates, and is invaded by a cellular 

 exudate, and in due course the glands and the tissue of the mucosa 

 and the muscularis mucosae are destroyed by coagulative necrosis, 

 with thrombosis of the vessels. This fibrinous or diphtheroid 

 membrane is at first most marked on the summits of the ridges, 

 and may not be found at the bottom between the ridges. It con- 

 tains large numbers of micro-organisms of varying characters, 

 while the depths of the submucosa may reveal accumulations of 



