PHYSIOLOGICAL ACTION OF NITROBENZENE VAPOR ON ANIMALS 429 
That this method for saturating air with nitrobenzene is practical 
was shown experimentally in the following way: A_ glass-stoppered 
U-tube containing a little nitrobenzene was dehydrated and weighed to 
constant weight. This U-tube was then placed in a constant temperature 
chamber, which was also a desiccator, with the final condensing tube, 
and air from this condensing tube was passed thru the U-tube for a given 
period of time. The U-tube was then reweighed, and the fact that it 
had neither lost nor gained in weight indicated that the air coming from 
the final condenser was saturated. 
Maintaining constant temperature 
A constant temperature +1 degree centigrade was maintained in the 
fumigation chamber by regulating the temperature of the room, it being 
found that a direct relation existed between these two temperatures. 
Histological technique 
In preparing sections for histological studies the following technique 
was employed. 
The animal was quickly and painlessly killed by piercing the heart with 
a scalpel, since it was important that death should be produced without the 
use of drugs and in a manner which would produce a minimum shock. 
The body was opened immediately, a cannula was connected with the aorta, 
and a warm (normal body temperature) isotonic saline solution was 
transfused until all the blood was washed out. The saline solution was 
immediately followed by the warm fixing fluid, which consisted of 4- 
per-cent formaldehyde in a saturated aqueous solution of corrosive sub- 
limate. The brain and the cord were then quickly dissected out, small 
pieces from each being placed directly in the fixing fluid and allowed 
to remain for twenty-four hours. The pieces were then washed in run- 
ing water for twenty-four hours, after which they were carried thru— 
90-, 60-, 70-, and 82-per-cent alcohol. They were allowed to remain in 
82-per-cent alcohol, to which was added a few drops of 5-per-cent alcoholic 
lodine, until the excess corrosive sublimate had been removed. The 
alcohol was changed twice a day for a time, and then as frequently as it 
became decolorized. The tissues were then dehydrated, cleared, 
embedded, and sectioned. The sections were cut 4 and 5 microns thick 
