PATHOGENIC BACTERIA. 307 



persons or of those suffering with other diseases, nor when the blood-serum 

 of a typhoid fever case is mixed with motile bacteria other than typhoid bacilli. 

 It has been observed iii the blood-serum of an infant born while the mother 

 was convalescing from typhoid fever. 



The agglutinating substance has been found in blister-serum and in the 

 milk of typhoid cases, in fluids from the serous cavities and inflammatory and 

 edematous areas in variable amounts, and occasionally in urine, bile and tears. 



The reaction may be obtained by adding blood-serum to a young bouillon- 

 culture of typhoid bacilli kept in the incubator, when the occurrence of agglutina- 

 tion becomes manifest by the collection of the bacteria into visible masses 

 or flocculi, which form a sediment. Most investigators prefer to watch the 

 results under the microscope, using an ordinary slide, or, better, the hanging- 

 drop. Young cultures — less than twenty-four hours old — ^in bouillon, and 

 kept in the incubator, may be used, or, better, cultures kept at room-tempera- 

 ture for twenty-four hours. Johnston and McTaggart recommend that the 

 bouillon cultures be freshly made each time from stock cultures on agar, 

 which need only occasionally be transplanted. Certain stocks of typhoid 

 bacilli seem especially suited to this reaction, and such a stock should be 

 secured. 



Blood-serum, blister-serum, fresh blood and dried blood have all been 

 tried with success. Blood dried on unglazed paper or cover-glasses as pro- 

 posed by Wyatt Johnston is extremely convenient. To perform the test it is 

 mixed with sterilized distilled water, bouillon or normal salt solution; the 

 objection to it lies in the difficulty of securing an accurate dilution. An ap- 

 proximate knowledge of the degree of dilution may be acquired by mixing 

 drops of dried blood of known volume with definite amounts of water, and 

 observing the tints. These should be kept in mind as standards. The dilu- 

 tion may be measured with the hemoglobinometer or with the pipette of the 

 hemocjftometer. The New York Board of Health have found blister-serum 

 satisfactory and easy to obtain. A little of the diluted serum is mixed on the 

 cover-glass with a definite amount of the fresh bouillon-culture, and is examined 

 as a hanging-drop. In a short time the characteristic clumping and loss of 

 motility occur. At the same time a drop of the culture alone, and a drop 

 of the culture mixed with normal serum, similarly diluted, should be examined 

 as controls. The dilutions used vary from i part of serum in 30 to i in 50. 

 The higher dilutions are more accurate. The time within which the reaction 

 occurs varies from a few minutes to one or two hours. With little dilution 

 the time should be short; with greater dilution it may be longer. Both ces- 

 sation of motility and clumping should take place. In a positive case the 

 reaction should be distinct. Normal blood sometimes exhibits agglutinative 

 properties in some degree. If the reaction in any case is not satisfactory, it 

 should be tried with a higher dilution, i to 50, and the result should be posi- 

 tive if the case is a genuine case of typhoid fever. 



The reaction usually appears between the seventh day and the end of the 



