272 BACTERIA PATHOGENIC TO MAN 



the diagnosis still remains in doubt, for the reaction is quantitative only, 

 and not qualitative. They concluded, nevertheless, that these investiga- 

 tions would render valuable assistance in the clinical diagnosis of cholera 

 and typhoid fever. 



Gruber-Widal Test. The first application of the use of serum, how- 

 ever, for the early diagnosis of typhoid fever on a more extensive 

 scale was made by Widal, and reported with great fulness and detail 

 in a communication published in June, 1896. Widal confirmed the 

 reaction as above described, proved that the agglutinative reaction 

 usually occurred early, elaborated the test, and proposed a method by 

 which it could be practically applied for diagnostic purposes. Since 

 then the serum test for the diagnosis of typhoid fever has come into 

 general use in bacteriological laboratories in all parts of the world, and 

 though the extravagant expectations raised at the time when Widal 

 first announced his method of applying this test have not been entirely 

 fulfilled, it has, nevertheless, proved to be of great assistance in the 

 diagnosis of obscure cases of the disease, and is now one of the recog- 

 nized tests for the differentiation of the typhoid bacillus. 



It should also be mentioned that to Wyatt Johnson, of Montreal, 

 belongs the credit of having brought this test more conspicuously before 

 the public, by introducing its use into municipal laboratories, suggesting 

 that dried blood should be employed in place of blood serum (Widal 

 having previously noticed that drying did not destroy the agglutinating 

 properties of typhoid blood) ; and that in October, 1896, the serum test 

 was regularly introduced in the New York Department of Health Labo- 

 ratory for the routine examination of the blood serum of suspected 

 cases of typhoid fever. Since then numerous health departments have 

 followed the example set by those of Montreal and New York. 



Use of Dried Blood. DIRECTIONS FOR PREPARING SPECIMENS OF 

 BLOOD. The skin covering the tip of the finger or the ear is thoroughly 

 cleansed, and is then pricked with a needle deeply enough to cause 

 several drops of blood to exude. Two fair-sized drops are then placed 

 on a glass slide, one near either end, and allowed to dry. Glazed paper 

 may also be employed, but it is not as good, for the blood soaks more 

 or less into it, and later, when it is dissolved, some of the paper fibre is 

 apt to be rubbed off with it. The slide is placed in a box for protection. 



PREPARATION OF SPECIMEN OF BLOOD FOR EXAMINATION. In pre- 

 paring the specimens for examination the dried blood, if accuracy is 

 desired, is first weighed and then brought into solution by adding to 

 it and mixing it with nine times the quantity of water; then a minute 

 drop of this decidedly reddish mixture is placed on a cover-glass, and 

 to it is added a similar drop of an eighteen to twenty-four-hour-old 

 bouillon culture of the typhoid bacillus, which, if it has a slight pellicle, 

 should be well shaken. The drops, after being mixed, should have a 

 faint reddish or pink tinge in this, the most highly concentrated serum 

 dilution. Higher dilutions are prepared by adding sterile broth, water, 

 or salt solution to the 1 : 5 blood mixture. The cover-glass with the 

 mixture on the surface is inverted over a hollow slide (the edges about 



