300 DISEASES OF TRUE INFECTION 



length of time, ])ut it is apt to change quickly at room temperature, and 

 for this reason a new l)atch of stain is usually made each day or as each 

 specimen is prepared for examination. A smear properly fixed on a 

 slide is taken up with a pair of forceps and completely covered with 

 stain. The slide is passed through the flame of a Bunsen burner several 

 times until steam arises from the heated stain, which is permitted to 

 remain on the smear for five to thirty seconds. The smear is then 

 washed in running water, and if the color of the smear is blue where the 

 brain tissue is thickest, and red where the smear is thin, the slide is 

 placed between filter-paper and dried. As soon as the slide is dry a 

 search is made for large nerve cells with a low-power lens under the 

 microscope. The protoplasm of the nerve cells should be stained a light 

 blue, the nucleus a shade of purple, and the nucleolus a dark blue. If 

 the cells are stained too deeply the stain may be weakened by the 

 addition of more distilled water or in heating the staining fluid on a 

 smear for a longer time, the intensity of the staining of the fuchsin will 

 be increased at the expense of the blue of the Loeffler's alkaline methylene 

 blue. "When a nerve cell is found properly stained, it is examined with 

 an oil immersion lens. Xegri bodies with this staining fluid show the 

 inner bodies a bluish black and the structure around the inner bodies a 

 maroon-red. They are found within the cell, outside of the nucleus of 

 the cytoplasm in the nerve cells of sections, but not infrequently in the 

 smear preparations, a few Negri bodies not Avithin the nerve cells are 

 seen, which have been forced out of the nerve cell as the smear is made. 

 In searching a smear for Negri bodies, only those bodies within the nerve 

 cells should be considered. 



In doubtful cases the disease can only be accurately diagnosed by 

 vaccination — that is to say, by the injection of small quantities of horn 

 of Ammon or a section of the cord, which have been diluted with distilled 

 water, and emulsified and filtered through fine linen. The following 

 methods are used at present: 



(1) The Intercranial Subdural Inoculation (Pasteur). — The inoc- 

 ulating material (1 or 2 drops of the emulsion) should be injected into 

 the dura mater of a dog or rabbit, after it has been trephined, by means 

 of a small hypodermic syringe, and the wound sewn up. The operation 

 is easily performed, and is especially valuable when the suspected animal 

 may have bitten not only other dogs, but man. As this inoculation 

 from the spinal matter of a suspected dog takes at least two or three 

 weeks, sometimes longer, the animal develops all the phenomena of the 

 disease, paralysis, etc., on the quiet. Leclainche recommends intra- 

 cerebral inoculation, that is, direct injection of the inoculating substance 

 into the brain itself; the persons bitten should not delay, while waiting 

 for development, but all measures should be taken as soon as possible. 



