AGGLUTINATIVE REACTIONS 289 



influence of specific bacteria or bacterial toxins. Among these we may differ- 

 entiate two classes: The antitoxic sera and the bactericidal sera; the first 

 variety is represented by the serum containing diphtheria antitoxin, the second 

 by the energetic bacteriolytic action of the blood serum in convalescence from 

 cholera. 



As a variety related to the last group the agglutinating serum may be 

 included, which occurs during the course of, and after recovery from, many 

 infections. We are most familiar with this condition in enteric fever, in 

 which it first led to valuable and practical diagnostic results. 



The essential part of the phenomenon is that, in a mixture of such serum 

 with typhoid bacilli in a culture medium, they are deprived of their motility 

 and clump, i. e., " agglutinate." To determine this fact a few drops of serum, 

 1 to 2 c.c, are sufficient, and these may be most easily obtained by centrifuga- 

 tion or sedimentation in thin glass tubes. The phenomenon may be demon- 

 strated macroscopically as well as microscopically {Gi-uher-Widal reaction). 

 In the former case, with nutritive bouillon after the addition of the serum, 

 we see how a profuse uniform turbid accumulation of typhoid bacilli clears 

 completely in from twelve to twenty-four hours, and a delicate flocculent 

 precipitate forms which, even by powerful shaking of the test-tube, can no 

 longer be disseminated. 



The microscopic test is carried out in the following manner : A drop of 

 the typhoid culture which is to be utilized for the test is arranged as a hanging 

 drop, so that we may convince ourselves of the active motility of the bacilli. 

 If serum in an exact proportion is then carefully added to the collection of 

 bacilli, and one drop is placed under the microscope in a positive reaction, 

 we notice even after a few minutes, at latest after a quarter of an hour, a 

 complete cessation of movement, a clumping of bacteria in large groups, as 

 well as an indistinctness in their outlines. 



[Another method is the following: A 3-inch test-tiibe of small caliber 

 is carried to the bedside of the patient together with a clean medicine dropper. 

 Ten drops of water are allowed to fall from this dropper into the test-tube. 

 The patient's ear is then punctured in the ordinary way and a full drop of 

 blood is sucked into the dropper and then expelled into the water in the 

 test-tube. The test-tube is then corked and carried to the laboratory where 

 the culture is kept, and one drop of the blood and water mixture is mixed 

 with one drop of the culture and examined between slide and cover. There 

 is no need of separating serum and corpuscles in this test ; the whole blood is 

 equally serviceable. 



For public health work the blood may be dried on tin foil, folded in, and 

 mailed to the State Laboratory where dilution is made by weight. This 

 method is extensively and most successfully used by the State Board of Health 

 in Michigan. — Ed.] . . 



The value of this reaction test can only be properly appreciated if it is 

 carried out with- certain precautions. First, we must assure ourselves of the 

 proper composition of the typhoid culture to be used in testing, and must be 

 sure that it is a fresh one, not older than a day. The serum requires, as 

 already stated, a corresponding dilution, because even normal serum if undi- 

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