GENUS BACTERIUM 243 



Where dilutions greater than 1-1,000 are made, a serum diluted 

 1-80 may be used to better advantage, unless the pipette employed is 

 very finely graduated. In this case the amount of diluted serum for 

 a certain dilution must be double that indicated in the table. 



The mixture thus prepared is placed in an incubator at 37 C. 

 for 24-30 hours. A temperature higher than 37 C. interferes with 

 the agglutination. 



Reaction. The reaction consists of a layer of the agglutinated 

 bacteria settling and covering the entire convexity at the bottom of 

 the tube. This film-like sediment may become so dense that it rolls 

 in at the periphery. The supernatant fluid becomes clear in the 

 lower dilutions, but in the higher ones the clarification may not be 

 complete, showing that all the bacteria have not become agglutinated. 

 This is further evinced by the fact that the layer is less dense in the 

 higher dilutions. The reaction may begin in six hours, but cannot 

 be considered complete until 24 to 72 hours have elapsed. Often, 

 however, a reaction appears in less than 24 hours. 



After the agglutination is completed, further standing produces 

 no visible change in the test-fluid. 



A negative result shows a small round concentrated spot of 

 sediment in the center of the convexity at the bottom of the tube, 

 the test-fluid remaining apparently unchanged even after several 

 weeks. 



The agglutination test has been made by the microscopic 

 method as in the Widal for typhoid fever. This laboratory 

 has found that agglutination sufficient to be determined micro- 

 scopically occurs often with very weak dilutions of the serum, 

 and not infrequently with that of healthy horses. It is possible 

 that the microscopic examination may be of assistance in 

 diagnosing the disease in man. It has not been trustworthy in 

 our hands with horses, although the method is used in certain 

 laboratories. 



Precipitation. According to Mohler 9 the precipitin reac- 

 tion of Konew is carried out in the following manner: 



"The blood taken from the jugular vein of the horse to be ex- 

 amined is collected in a glass container and then allowed to remain 

 at room or incubator temperature. The separated serum which is 

 thus obtained serves as the second necessary fluid for the precipita- 

 tion reaction. In order to produce the reaction one cubic centimeter 



9 Mohler. Proc. of the Amer. Vet. Med. Assn., 1910, p. 323. 



