404 The Study of Zoölogy in Germany. [July, 
tilled water, as long as there is any blue left. To make the 
“ warm” injection mass take twenty-five parts of the Prussian- 
blue solution and one part gelatine. The latter must be of the 
finest quality, as otherwise it produces a granular precipitate 
which renders it useless for histological purposes. Put the gela- 
tine to soak for half an hour in distilled water, then remove and 
wash it; place it ina glass vessel and warm it in a water-bath, 
when it will melt in the water it has absorbed. The Prussian 
blue is put in another vessel in the same water-bath, so that: the 
two liquids are at the same temperature. Pour the gelatine, 
little by little, into the blue, stirring constantly with a glass rod. 
Keep on warming and stirring until the granular precipitate 
formed at first disappears. Upon being filtered through a piece of 
clean flannel, the mass is ready for use. 
It requires only to be slightly warmed to become liquid, and 
the organ to be injected does not need to be heated to so high a 
temperature as is necessary in using many other injection masses; 
there is, therefore, no danger of injuring the tissues by sub- 
jecting them to too high a temperature. The injection should 
be continued until a little while after the mass begins to come 
out through the veins, in order to allow all the capillaries time to 
fill themselves. When the injection is finished, the organ may 
be placed to advantage for twenty-four hours in a 2 to 1000 
solution of bichromate of potassium in distilled water, and then 
be removed to alcohol; or it may be put at once in alcohol, and, 
when hardened, sections made of it. The sections should be 
pretty thick, and may or may not be stained as is desired. If 
too thin, they do not show the connections of the vessels. 
As an example of the clearness with which 
= the blood-vessels may be traced in a suc 
l a section 
rying the blood-vessels. There is a net-work 
of small arteries in the cutis, and from this 
—> there pass up from three to five fain beanii 
—=— into each papilla, and form by division ur 
=> inter-communication a wide capillary n 
HUMAN LIP. work. One or several fine capillaries ben 
