THE TYPHOID HAC/LLUS 275 



blister so small that it is practically painless and harmless. The serum 

 obtained is clear and admirably suited for the test. 



ADVANTAGES AND DISADVANTAGES OF SERUM, DRIED BLOOD AND 

 FLUID BLOOD FOR THE SERUM TEST. The dried blood is easily and 

 quickly obtained, and does not deteriorate or become contaminated by 

 bacterial growth. It is readily transported, and seems to be of nearly 

 equal strength with the serum in its agglutinating properties. It must 

 in use, however, be diluted with at least five times its bulk of water, 

 otherwise it is too viscid to be properly employed. The amount of 

 dilution can only be determined roughly by the color of the resulting 

 mixture, for it is impossible to estimate accurately the amount of dried 

 blood from the size of the drop, and it is too much trouble to weigh it 

 accurately. Serum, on the other hand, can be used in any dilution 

 desired, varying from a mixture which contains equal parts of serum 

 and broth culture to that containing 1 part of serum to 100 parts of 

 culture or more, and this can be exactly measured by a graduated pipette, 

 or, roughly, by a measured platinum loop. The disadvantages in the use 

 of serum are entirely due to the slight difficulty in collecting and trans- 

 porting it, and the delay in obtaining it when a blister is employed. If 

 the serum is obtained from blood after clotting has occurred a greater 

 quantity of blood must be drawn than is necessary when the dried-blood 

 method is used; if it is obtained from a blister, a delay of six to eighteen 

 hours is required. The transportation of the serum in capillary tubes 

 presents no difficulties if tubes of sufficiently thick and tough glass are 

 employed and placed in tiny wooden boxes. For scientific investiga- 

 tions and for accurate results, particularly in obscure cases, the use of 

 fluid serum is to be preferred to dried blood. Practically, however, the 

 results are nearly as good for diagnostic purposes from the dried blood 

 as from the serum. 



FLUID BLOOD. When properly obtained this gives good results. 

 The Thoma-Zeiss blood pipette is very useful. Lance finger-tip or 

 ear and draw the blood into the pipette to the mark 0.5. Then distilled 

 wafer is sucked up in sufficient amount to make the desired solution. 

 One loop of this is added to one loop of bouillon culture. 



THE CULTURE TO BE EMPLOYED. It is important that the culture 

 employed for serum-tests should be a suitable one, for although all 

 cultures show the reaction, yet some respond much better and in 

 higher dilutions than others. Cultures freshly obtained from typhoid 

 cases are not as sensitive as those grown for some time on nutrient 

 media. Decrease in virulence is apt to be accompanied by increase of 

 capacity for agglutination. For the past seven years we have used a 

 culture obtained from Pfeiffer. A broth culture of the typhoid bacillus 

 developed at 25 to 35 C., not over twenty-four hours old, in which the 

 bacilli are isolated and actively motile, has been found to give us the 

 most satisfactory results. Cultures grown at temperatures over 38 C. 

 are not apt to agglutinate so well as those grown at lower temperatures. 

 Stock cultures of typhoid bacilli can be preserved on nutrient agar in 

 sealed tubes and kept in the ice-box. These remain alive for months or 



