400 TYPHOID FEVER 



Agglutination. All the above-mentioned observers agree re- 

 garding the agglutination of this bacillus by the serum that is, 

 in the cases of dysentery from which the organism can be cul- 

 tivated, and the reaction is of diagnostic value. The reaction 

 may appear on the second day, and is most marked after from 

 six to seven days in the acute cases ; it is usually given in a 

 dilution of from one in twenty to one in fifty within an hour, 

 though sometimes much higher dilutions give a positive result. 

 In the more chronic cases the reaction is less marked, and here 

 the sedimentation method is to be preferred. It is difficult to 

 make any general statements with regard to the effects of 

 dysenteric sera on the different strains of the bacilli, but it may 

 be said that generally a serum agglutinates the strain which 

 produced it and the other strains of the same group in higher 

 dilutions than it does the strains of the other group. Many 

 observers have found that the serum from a case associated with 

 strains of the Shiga-Kruse group has not agglutinated strains of 

 the Flexner group, and corresponding observations have been 

 made in cases associated with the Flexner group. Often the 

 sera of animals immunised with bacilli have been used for such 

 tests, but apparently great care must be exercised in basing 

 diagnoses on such observations, as the sera vary in different 

 instances as regards their action on strains allied to that used 

 for injection. The agglutination method is not so useful for 

 the differentiation of strains as it is in the case of the para- 

 typhoid group, and, when the underlying reaction is taken 

 advantage of, the absorption technique should be employed. 

 Agglutination of the organism has not been obtained with 

 serum from cases other than those of dysentery, nor has a 

 similar bacillus been cultivated from such sources. The reaction 

 is also absent in those cases of dysentery which are manifestly 

 of amoebic nature. 



Pathogenic Properties. The organism is pathogenic in guinea- 

 pigs and other laboratory animals, but, in these, characteristic 

 changes in the intestine are often awanting. Shiga, however, 

 obtained such effects by introducing the organism into the 

 stomach of young cats and dogs, and confirmatory results were 

 obtained by Flexner. Such attempts have been specially suc- 

 cessful when the virulence of the organism has been previously 

 exalted by intraperitoneal passage. In two cases, apparently 

 well authenticated, a dysenteric condition has followed in the 

 human subject from ingestion of pure cultures of the organism. 



It is probable that in the action of the bacillus a toxin is 

 concerned. If the organism be grown for two or three weeks in 



