These bacilli are encountered in sporadic cases or in different epidemics without an apparant preponderance of any one type. Thus two or more types may be present in the one case. Nor do they bear any relation to the clinical type (mild or severe) with which they are associated.
In the Journal of Experimental Pathology (1898) there appears an account of a limited but very fatal epidemic in the United States in which Bacillus pyocyaneus was found. Calmette and Maggiora report that they also have encountered this bacterium in dysentery, as well as in infantile diarrhœa.
The case-mortality from bacillary dysentery varies greatly in different parts of the world, depending to a great extent on the age and social status of those attacked. In Japan it is about 24 per cent.; in French epidemics it has been as high as 50 per cent.; in Fiji it is about 13 per cent, at the present day, though formerly a much more fatal form existed. It is especially fatal to children, in whom it is commonly found, and in whom the toxic effects are most marked; death being due to heart failure, probably consequent on toxic absorption.
Pathology of bacillary dysentery.— The large intestine is the seat of the affection; in some cases the last few feet of the ileum also may be attacked. In early cases the gut wall is thickened and infiltrated, the mucous membrane œdematous and of a cherry-red colour showing small yellow superficial ulcers along the exposed borders and folds. In severe cases, or cases in which the disease has lasted for some time, the mucous membrane may be entirely gangrenous, of a bright-green colour, and forming what appears to be a false membrane on the surface of the bowel. This change extends down to the anus, though the cæcum and the sigmoid flexure are the areas most severely attacked. The puckered or stippled appearance of this green layer is very characteristic. At a further stage large pieces of mucous membrane slough away, leaving ragged irregular ulcers and exposing the muscular coat. The process appears to start from the solitary lymphoid
