510 Typhoid Fever 



by its own weight upon bibulous paper, where it is dried. When the 

 test is to be made, this dried blood-drop is dissolved in as many drops 

 of water or other diluent as will give the necessary dilution. Unfor- 

 tunately the blood quickly coagulates in the dropper. 



Some have successfully employed the pipet used for counting leu- 

 kocytes in making the dilutions. 



Delepine suggested a method that can be employed both in the 

 laboratory and at the bedside. A drop of blood or serum is picked 

 up with the bacteriologist's platinum loop, placed upon a glass slide, 

 and mixed with nine, nineteen, or thirty-nine, etc., similar drops of 

 the culture to be used, the mixtures forming dilutions of 1 : 10, 1 : 20, 

 1 : 40, etc. 



I * have used capillary glass tubes of equal size, which, when al- 

 lowed to draw up the blood from a prick on the finger-tip, will contain 

 a quantity of blood easily estimated from the length of the column 

 in the tube. Knowing the quantity of contained blood, it is easy to 

 estimate how much fluid culture one must add to make a definite 

 dilution. The tube is crushed and stirred in the diluting culture, so 

 that none of the blood is lost. 



Hewlett and Sydney f recommend a similar, probably more exact, 

 method. 



The majority of observers use bouillon cultures of the typhoid 

 bacillus for making the test, but I prefer fresh agar-agar cultures 

 suspended in sterile clean water, rather than bouillon cultures, because 

 of the larger number of bacteria they contain, the consequently greater 

 number of agglutinations formed, and the readiness with which they 

 are found upon microscopic examination. It is necessary, however, to 

 make a microscopic examination before adding the serum or blood, 

 in order to be sure that there are no natural clumps of bacteria present 

 to simulate the specific agglutination. This is of great importance. 

 The natural clumps of bacilli are more apt to occur in cultures grown 

 upon fresh, moist agar-agar than upon that kept for a short time until 

 the surface has become partially dried. 



Errors are most apt to occur when too concentrated dilutions of 

 the typhoid blood or serum are used, and it is only in cases in which 

 sufficient dilutions of the serum produce agglutination that a positive 

 diagnosis of typhoid can be made. 



Stern J concluded that the dilution should be 1 : 100, or even 1 : 200 ; 

 Widal, however, found 1 : 60 sufficient. Dilutions of 1 : 50 are most 

 satisfactory for routine work. 



Welch says: "From the observations thus far reported, although 

 they are insufficient in number for definite conclusions, there would 

 seem to be only a small liability of failure to recognize genuine typhoid 

 cases by resorting to dilutions of 1 : 40 or 1 : 50, but unquestionably 

 a few would escape recognition, and for this reason lower dilutions 

 should also be used, and if those between 1:10 and 1 : 50 give decided 

 reaction there should be at least suspicion of typhoid. It is not, there- 

 fore, to be recommended that one make the test with only high dilu- 

 tions, such as 1 : 50. The negative result of the preliminary test with 

 equal parts of serum and culture suffices to exclude typhoid reaction. 

 The examination, if positive, may then be made with a low dilution 

 of the serum, and for this Widal's recommendation of 1 : 10 or 1 : 15 

 may well be adopted. If with this dilution the microscopic reaction 

 is complete and almost immediate, as is often the case, there is prac- 



* "New York Med. Jour.," Sept. 25, 1897. 



f'Brit. Med. Jour.," April 28, 1900. 



J "Centralbl. f. innere Med.," Dec. 5, 1896. 



