556 THE DIGESTIVE SYSTEM. 



Amoeba excites at first a moderate exudative and productive inflam- 

 mation followed by necrosis. Thus ulcers are formed. The ulcers may 

 be superficial or deep, sometimes extending to the peritoneum ; they en- 

 large by infiltration and necrosis at their edges, so that extensive destruc- 

 tion of the mucous membrane may occur. The amoeba may be present 

 in the connective tissue at the base or sides of the ulcers. Not infre- 

 quently, owing to bacterial infection from the intestinal contents, vary- 

 ing degrees of suppurative inflammation may complicate the lesion. 



Necrotic and suppurative processes may be set up in the liver (see 

 page 593) and in the right lung, and in these lesions the amo3ba may be 

 found. 



(6) ACUTE INFECTIOUS COLITIS WITH BACTERIAL EXCITANTS. 

 The lesions in those forms of infectious colitis which are not associated 

 with amoeba are varied, and it is not yet possible to give a very precise 

 morphological characterization of them. In general it may be said that 

 the lesion when pronounced is pseudo-membranous, exudative, and necro- 

 tic, with more or less ulceration of the mucosa and subniucosa. 



The earlier bacterial studies of the various types of infectious colitis 

 dysentery tropical, epidemic, sporadic, or pseudo-membranous, gave 

 little definite data. Many bacteria were found, most of them of species 

 not infrequently present in the normal intestine. In 1897, however, 

 Shiga made a careful study of a series of cases in a serious dysentery 

 epidemic occurring at that time in Japan. Shiga found constantly in 

 these cases a bacillus Bacillus dysenteries not normally present and 

 pathogenic for animals, which gave agglutinative reactions with the serum 

 of the dysentery patients. This bacillus was formerly regarded as simi- 

 lar to the typhoid bacillus, but can now be readily differentiated from it. 1 

 Two years later Kruse found a similar bacillus in cases of dysentery oc- 

 curring in Germany, and Flexner and Strong have found one which they 

 believe to be identical in the Philippines. It has since been found in nu- 

 merous instances in the United States. 



Considerable doubt has arisen regarding the significance of many of 

 the later determinations owing to the fact that until recently some of the 

 distinctive biological characters were not generally known, and that the 

 agglutination reactions, if not carried out with extreme care, may lead 

 the observer astray. 



We cannot enter here upon the details of the various studies of this 

 subject. It at present seems likely that the Shiga bacillus is the excitant 

 of some forms at least of tropical and epidemic or sporadic dysentery. 

 Whether the occurrence which has been described of this bacillus or va- 

 riants of it, in other forms of intestinal disorder, such as some types of 

 infantile diarrhoea, is of significance or not, it is yet too early to say. 



While the value of protective serum prepared by animal inoculations 

 of Shiga's bacillus has been claimed, the evidence is yet too meagre to 

 permit of final judgment." 



J See Hiss and Russell, Med. News, Feb. 14th, 1903. 



8 For a general statement of forms and lesions of dysentery and its relationship to 



