Negri bodies 



SMEAR PREPARATIONS FROM CUT SURFACES 



75 



In every other respect these smears are 

 treated as though they had been prepared 

 from a fluid material (see last chapter) but 



a single typical preparation applying one 

 of these techniques will be given. 



Typical Example 



Demonstration of Negri Bodies by the Method of Dawson 1934 



The detection of Negri bodies is, of 

 course, used in the diagnosis of rabies. A 

 method for the demonstration of these 

 bodies in sections is described in Chapter 

 21, and the method here described is in- 

 tended less for permanent preparations 

 than for a rapid diagnostic procedure. 

 The description referred to contains de- 

 tailed directions for the dissection of the 

 horn of Amnion, which is the portion of 

 the brain usually selected for these tests. 

 We will assume, therefore, that the worker 

 has dissected, following the necessary pre- 

 cautions as to his own safety, the brain 

 of the diagnostic guinea pig in such a 

 manner as to expose the horn of Ammon. 



For the preparation of paraffin sections, 

 the horn of Ammon is divided into small 

 pieces, but for the preparation of smears 

 it must be kept whole and a sharp razor 

 used to trim away about the lower third 

 leaving a freshly cut surface. If there is 

 any quantity of extravasated blood pres- 

 ent, it must be washed off with a gentle 

 stream of normal saline or it will tend to 

 obscure the picture. 



To prepare the smear preparations there 

 are required an adequate quantity of clean 

 shdes, a supply of methanol, a 2 % solution 

 of phloxine, and a quantity of Lofiler's 

 polychrome methylene blue. The prepara- 

 tion of the polychrome methylene blue 

 solution is described in Chapter 20 (DS 

 11.44 Lofiier 1890) and need not be re- 

 peated here. It is convenient to have the 

 methanol and methj'lene blue solutions in 

 drop bottles and to have the 2% phloxine 

 and the 20% alcohol in coplin jars. If the 

 slides are to be filed for reference, rather 

 than used immediately for diagnosis, it is 

 also desirable to have some neutral 

 mountant (Chapter 26, M 23.1) 



The entire horn of Ammon is then taken 

 and dabbed once or twice in the center of 

 one of the clean shdes. If one endeavors to 

 smear it, too much material usually (;omes 

 off; but the vertical dabbing motion will 



provide a sufficiently thick film which, 

 when moist, should appear as no more 

 than a slight clouding of the surface of the 

 slide. The shde is then waved gently back- 

 ward and forward until it appears to be 

 just about to dry. The material will be 

 lost if methanol is added to it while it is 

 completely wet, and the material will be 

 distorted if it is permitted to become en- 

 tirely dry; but only a little experience is 

 necessary to enable one to adjudge the 

 exact moment at which methanol should 

 be dropped on the smear from the drop 

 bottle. The shde may then be placed on 

 one side to dry, if it is to be used immedi- 

 ately; it should be dropped into a cophn 

 jar of methanol if it is not to be stained 

 for, say, half an hour. 



When the slides are to be stained they 

 are waved in the air until the methanol 

 has evaporated and then dropped into the 

 2 % phloxine where they remain from two 

 to five minutes. Upon being withdrawn 

 from the phloxine, a stream of water from 

 a wash bottle should be used very gently 

 to remove the excess phloxine, the slide 

 drained by its corner onto filter paper, 

 and the polychrome methylene blue 

 dropped onto the surface from a drop 

 bottle. The methylene blue is left in place 

 for 15 seconds, washed off with a stream 

 of water from the wash bottle, and the 

 slide then dropped into 20% alcohol where 

 it may be left until no more color comes 

 away. It may remain in the alcohol for 

 10 or 15 minutes without damage. 



If the slide is required for immediate 

 examination, nothing remains to be done 

 save to remove it from the 20% alcohol, 

 wave it about in the air until it is dry, and 

 then examine it under the microscope 

 with an oil immersion lens. If, however, 

 the shde is to be filed for permanent refer- 

 ence, a drop of neutral mountant should 

 be placed on the smear as soon as it has 

 been dried and a covershp added. 



