74. The Blood Vessels of the Prostate Gland 
filled the arteries, capillaries, and veins; the blue passed into the arteries 
and arterioles, displacing the gelatine and filling them, but was stopped 
at the capillaries because the ultramarine-blue granules were too large 
to enter them. Ina specimen thus prepared the arteries appear blue, and 
the capillaries and veins red. This is shown in Figure 1, with colors 
reversed, in order to present the conventional appearance. As it was 
impossible to get a perfectly complete injection in one specimen, several 
of the best were selected and the gaps filled in, with the results as shown 
in Figure 1. One section, however, is remarkably beautiful and presents 
a picture very closely resembling that seen in this figure. 
In order to map out the complete network of arteries surrounding a 
separate lobule, I injected them with Prussian blue, then opened the 
urethra, and injected carmine gelatine into a prostatic duct through a 
very fine blunt hypodermic needle. A specimen made in this way is shown 
in Figure 2 where the ducts are represented in brown. The capillaries 
were studied in a specimen which had been completely injected with car- 
mine gelatine. A very thin section of this was stained with iron hzema- 
toxylin, and is shown in Figure 3. The basement membrane is arti- 
ficially tinted with yellow so as to make it visible. 
The technique of the injecting is rendered difficult by the fact that the 
situation of the gland in the pelvis is somewhat remote. In all, about 
75 dogs were used before a complete circulation cycle could be seen. 
Cinnabar, lampblack, and various other substances were tried, but they 
did not prove as good as the combination of carmine gelatine followed by 
ultramarine-blue gelatine. 
When the ordinary directions for preparing carmine gelatine were fol- 
lowed, it always proved difficult to get a perfectly transparent substance. 
The trouble is connected with the neutralization of the ammonia by the 
acetic acid. The gelatine should be rendered practically neutral, but 
if the reaction is carried the least bit too far, the solution becomes 
cloudy. Sometimes two drops of the acetic acid are sufficient to make 
turbid a whole htre of the prepared carmine. After a good many 
trials, the following method was adopted: ‘Take 10 cc. of the ordi- 
nary laboratory ammonia and dilute with 40 cc. of distilled water, 
then determine by titration the exact amount of the laboratory acetic 
acid which will neutralize it. After this determination has been made, 
10 grms. of pure carmine are rubbed up with 50 ce. of distilled water ; 
then 25 ce. of the ordinary ammonia are measured, and a few drops at a 
time are poured into the carmine mixture which is kept constantly rubbed 
up. This process is very closely watched, and the ammonia is gradually 
added until the carmine is completely dissolved, and the mixture becomes 
