OF MICROSCOPIC OBJECTS. 129 



it is very difficult (if not impossible) to accomplish much without 

 some knowledge of anatomy. 



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 pres- 

 sure 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 indi- 

 cated above. 



Since writing the above, Mr. J. Gr. 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 l-2000th of an inch in 

 diameter, and present a clear outline with one-fifth objective. 

 There is no extravasation, neither does the colouring matter show 

 any grain except when a very high power is employed. The fol- 

 lowing is our process : 



Take 180 grains best carmine ; J fluid ounce of ammonia, com- 

 mercial strength, viz., 0*92, or 15 ammonia meter; 3 or 4 ounces 

 distilled water. Put these into a small flask, and allow them to 



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