324 THOMAS J. HELDT 



glass slides respectively. The larger container was now filled 

 with ice and salt which was carefully packed about the smaller 

 vessel. When the temperature of the alcohol and the fixative 

 had been reduced to — 8°C. or lower, carbon dioxide snow was 

 added to the 95 per cent alcohol in the smaller of the containers 

 until the temperature was further reduced to —20° to — 50°C. 

 At this time the dog was immediately killed and smears made 

 on the cold slides upon w^hich they froze instantly. Then they 

 were quickly dropped into the cold fixative. The time consumed 

 in making the preparations was judged from the instant of decap- 

 itation to the exact moment the fixative received the smear. 

 The smears were left in the fixative for a time varying as above 

 noted. When the time was prolonged the whole of course ac- 

 quired room temperature in the meantime. 



In those cases where preparations were made at various inter- 

 vals after death the cord segment was in all cases kept under 

 the ordinary conditions of the laboratory and at ordinary room 

 temperature. The majority of the long post-mortem interval 

 preparations, however, were made during the winter months so 

 it may be said that the temperature of the laboratory ranged 

 from 5° to 23°C. 



The staining methods used are comparatively simple. For the 

 staining of the Nissl's bodies the method outlined by Dolley ('11) 

 was used. The method is in the main as follows: The smears 

 fixed in 96 per cent alcohol are brought through a series of 

 alcohols of decreasing strength to distilled water, then stained 

 with warm (ca. 40°C.) erythrosin for three minutes, and well 

 washed in water. They are then brought into a 1 per cent 

 aqueous solution of toluidin-blue for five to eight minutes, again 

 well washed in water, after which they are dipped in 95 per cent 

 alcohol and differentiated, until the Nissl's bodies and nuclear 

 structures are clearly defined, in a mixture of 96 per cent alcohol 

 9 parts, anilin oil 1 part. The differentiation is stopped by 

 bringing the slide into absolute alcohol from which it is brought 

 into xylol and mounted in Canada-balsam or damar. 



To stain the neurofibrillae, London's method was followed. 

 The method is essentially the following : After fixation, the smears 



