858 The American Naturalist. [Octoher, 
When small transparent pieces of tissue were to be examined, they 
were fixed in a saturated solution of picrate of ammonia in distilled 
water from 2—4 hours and were then mounted in a mixture of equal 
parts of pure glycerine and distilled water to which a small quantity of 
picrate of ammonia is added. When opaque or large pieces were fixed 
in this way they were sectioned by the freezing method. After fixing 
in the picrate of ammonia, the tissue was placed in a saturated solution 
of sugar for one hour and was then transferred to a piece of blotting 
paper to remove the syrup from its surface. It was then placed in a 
thick solution of gum arabic for fifteen minutes and then transferred 
to the plate of the freezing microtome where it was frozen by means of 
liquid carbonic acid. The sections were mounted in dilute glycerine as 
in the other case. The principal advantage of this method is its rapid- 
ity, but neither serial sections nor those of equal thickness can be 
obtained. 
In order to obtain serial sections by the paraffine method, the tissues 
were fixed in Berthe’s sara 
For vertebrates For invertebrates : 
Molybdate of ammonia, i gram. Molybdate of ammonia, 1 gram. 
Distilled water, 10c. Distilled water, 10 c. c. 
Hydrochloric acid, 1 a Peroxide of Hydrogen, } c. c. 
Peroxide of ritigi, le. é: 
A different formula 1s used for tissues of invertebrates as less oxygen 
is required than for vertebrates. The fixing fluid must be cooled on 
ice before placing the tissue in it. After remaining in the cold fixing 
fluid for from 2-4 hours the tissue is thoroughly washed with cold 
water which generally takes about two hours although it has been con- 
tinued for twelve hours without injury 
It is necessary to remove all the molybdate of ammonia by thorough 
washing if permanent preparations are to be secured. 
The tissue is then passed rapidly, ten to fifteen minutes in each, 
through the ordinary grades of alcohol to absolute, all being kept cold 
with ice. The tissue should be left in the absolute alcohol for about 
two hours at a freezing temperature and the alcohol be changed several 
times. The stain is dissolved by dilute alcohol at ordinary tempera- 
tures. 
Dr. Huber’s plan of placing the tissue directly in cold absolute 
alcohol on removing it from the water and changing several times for 
a period of two hours, gave good results. 
2 Archiv. f. Mikros., Anat. Bd. 44, Heft 4. 
