BACTERIA IN WATER 63 



6. Widal 's Reaction. Mix a loopf ul of blood from a patient 

 suspected of typhoid fever with a loopful of young typhoid 

 broth culture in a hanging drop on a hollow ground slide. 

 Cover with a cover glass and examine under ^-inch objective. 

 If the patient is really suffering from typhoid, there will ap- 

 pear in the hanging drop two marked characteristics, viz., 

 agglutination and immotility. This aggregation, together 

 with loss of motility, is believed to be due to the inhibitory 

 action of certain bacillary products in the blood of patients 

 suffering from the disease. The test may be applied in various 

 ways, and its successful issue depends upon one or two small 

 points in technique into which we cannot enter here, but 

 which the reader will find dealt with in the appendix. 



7. Flagella-staining. Special methods must be adopted 

 for staining the flagella of Bacillus typhosus and B. coli. The 

 cover glasses should be absolutely clean, the cultures young 

 (say eighteen hours old), and a diluted emulsion with dis- 

 tilled water must be made in a watch-glass in order to get 

 bacilli discrete and isolated enough. Van Ermengem s 

 Method is as follows : — Place a loopful of the emulsion 

 on a clean cover glass and dry it in the air, fixing it lastly 

 by passing it once or twice through the flame of a Bunsen 

 burner. Place films for thirty minutes in a solution of one 

 part boric acid (2 per cent.) and two parts of tannin (15.25 

 per cent.), which also contains four or five drops of glacial 

 acetic acid to every 100 cc. of the mixture. Wash in 

 distilled water and alcohol. Then place for five to ten seconds 

 in a 25.5 per cent, solution of silver nitrate. Immediately 

 thereafter, and without washing, treat the cover glass to the 

 following solution for two or three seconds : gallic acid, five 

 grams; tannin, three grams; fused potassium acetate, ten 

 grams ; distilled water, 350 cc. After this place in a fresh 

 capsule of silver nitrate until the film begins to turn black. 

 Wash in distilled water, dry, and mount. The process con- 

 tracts the bacilli somewhat, but the flagella stain well. 



