38. I may here mention that the transparent injections sent over from the Continent are beautifully executed by Hyrtl of Vienna (who states that the injected fluid is composed 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 one 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 which renders the arteries impervious to the coloured fluid afterwards injected. 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 sufficient 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 process:-- Take 180 grains best carmine. ½ fluid ounce of ammonia, commercial strength, viz., 0·92, or 15° ammonia meter. 3 or 4 ounces distilled water. Put these into a small flask, and allow them to digest without heat from twenty-four to thirty-six hours, or until the carmine is dissolved. Then take a Winchester quart bottle, and with a diamond mark the spot to which sixteen ounces of water extend. The coloured solution must be filtered into the bottle, and to this pure water should be added until the whole is equal to sixteen ounces.