io6 AIDS TO BACTERIOLOGY 



sufficient. Time and dilutions should always be recorded. 

 A positive reaction with a 1 in 80 dilution would in almost 

 all cases indicate the bacillus to be either specific for the 

 serum or very nearly so. It sometimes happens that 

 agglutination is obtained with a certain dilution but not 

 with a lower one, e.g., the 1 in 50 may be positive and 

 one of 1 in 16 may be negative. Such ' zone reactions' 

 are very rare. 



The agglutination method is very satisfactory. It is 

 not obtained until about the seventh day of fever, is 

 rarely intermittent, and a negative result should not be 

 accepted unless repeated three or four times at intervals 

 of a few days; it is rarely absent throughout the course of 

 the disease, and in such cases the disease is frequently 

 severe. The reaction persists for years after an attack, 

 and, therefore, before applying the test a previous attack 

 should, if possible, be excluded. Inoculation with 

 Wright's vaccine also causes the blood of the inoculated 

 to acquire agglutinative properties. Pyrexia leads to a 

 diminution or disappearance of inoculation agglutinins, 

 and Tidy says that a positive Widal reaction after the 

 sixth day of pyrexia is as definite a proof of B. typhosus 

 infection in an inoculated as in an uninoculated man. 

 Delepine isolated a strain of typhoid bacillus, designated 

 as 7120, which clumped with the serum of an active case 

 of typhoid, but not with the serum of an artificially 

 inoculated person. The blood in paratyphoid infections 

 may sometimes agglutinate the typhoid bacillus, but 

 usually only in low dilution. Agglutometers for perform- 

 ing the test by macroscopical observation with dead 

 typhoid bacilli are sold. 



Ophthalmo-Diagnosis. Chantemesse applies typhoid 

 toxins to the conjunctiva a reaction analogous to Cal- 

 mette's tuberculin conjunctival reaction. 



Cutaneous Reaction. Deehan applies a drop of fluid 

 containing the standardised toxin to the skin, and then 

 makes a slight abrasion with a lancet under the drop. 

 The reaction, which does not cause the patients any 

 discomfort, is supposed to be specific. 



Cultivation from Faeces and Urine. Surface-plate 

 cultures (p. 237) on Conradi-Drigalski agar, MacConkey's 

 lactose bile-salt agar or malachite-green agar are made 

 with the material, which should be as fresh as possible. 



