OF MICROSCOPIC OBJECTS. 191 
posed of gelatine and carmine), Dr. Oschatz of Berlin, 
the Microscopic Institute of Wabern, Schaffer and Co. of 
Magdeburg, and others. Some of these will bear examining 
with a high power. A friend informs me that he measured 
a vessel in a rat’s tongue by Hyrtl, which was 1-7200th 
of an inch in diameter, and had a clear outline with quarter- 
inch objective. He has also made many experiments with 
the same materials, but has as yet failed in producing 
perfectly distinct outlines, there being a tendency of the 
colouring matter (magenta, carmine, &c.) to diffuse itself 
through the coats of the vessels into the surrounding tissues, 
although he has varied the pressure from half a pound to 
sixty pounds. He believes the vessels are first washed out 
' (injected with warm water and pressure applied), then some 
fluid introduced, probably solution of tannin, which renders. 
the arteries impervious to the coloured fluid afterwards in- 
jected. 
39. He finds that after washing out the vessels as above, 
the injecting fluid is much more easily introduced. He has 
used a strong solution of gallic acid previously to injecting 
with the colouring matter (in one experiment only), and the 
result was satisfactory. He puts the query,—Might not 
carbolic acid have a similar effect? He has often used it 
with injections to preserve the specimens, but not in suf- 
ficient quantity to act in the way indicated above. 
Since writing the above, Mr. J. G. Dale, F.C.S., and I 
have made numerous experiments with carmine injection, 
and have at length been favoured with what we deem 
success. Some of the vessels in a kitten lately injected do 
not exceed 1-2000th of an inch in diameter, and present a 
clear outline with one-fifth objective. There is no extra- 
vasation, neither does the colouring matter show any grain 
except when a very high power is employed. The following 
is our pracess :— 
