266 IMMUNOWGICAL METHODS OF DIAGNOSIS 



glass beads, in the ice box. In this manner the material will keep 

 for months, and can be used either for the microscopic test, in which 

 case the time of examination should be extended to two hours, or 

 it may be employed in the macroscopic test described below. 



Macroscopic Method. This method is just as exact as the micro- 

 scopic method, and is in a manner less apt to lead to confusion; 

 somewhat larger amounts of blood, however, are required (1 c.c.). 

 The serum is diluted in the same proportions as described above. 

 Equal quantities (0.25 c.c.) are then placed in small tubes, such as 

 the collecting tubes figured in Plate III, and treated with equal 

 volumes of the bacterial emulsion. These tubes together with a 

 control of equal volumes of saline and bacterial emulsion are placed 

 in the incubator, or some other warm place, and are examined after 

 twelve to twenty-four hours. If the reaction is positive the bacteria 

 in the serum tubes will have settled to the bottom, leaving the super- 

 natant fluid almost clear, thus contrasting sharply with the control 

 which is still as turbid as it was in the beginning. 



RESULTS. While a positive Widal reaction may be obtained as 

 early as the first day of the disease, meaning thereby the first day that 

 the patient spends in bed, or the fifth of general malaise, such an occur- 

 rence must be viewed as a great rarity. In the vast majority of cases 

 a positive result is obtained only after the fifth or sixth day in bed. 

 As the likelihood of positive bacteriological findings is greatest during 

 the first week of the disease, an examination in this direction may at 

 this time well take precedence over the agglutination test. During 

 the second week, when the value of the two methods is on a par, con- 

 venience may decide which one is to be employed. After this, how- 

 ever, the agglutination test should be given the preference. Experi- 

 ence has shown that a positive reaction may be obtained in practically 

 all cases of true typhoid fever, but it is clear from what has been 

 said that much depends upon the period of the disease at which the 

 examination is made. The production of agglutiniris evidently 

 does not begin at the same time in all cases, and does not 

 become fully established until after the disease has progressed 

 for a certain length of time. It may happen, indeed, that a positive 

 reaction is not obtained until convalescence, or even until a subse- 

 quent relapse occurs. For this reason it is advisable to repeat the 

 examination at frequent intervals, if on first trial a negative 

 result is obtained. Intermittence of the reaction, moreover, is 



