OF MICROSCOPIC OBJECTS. 191 



posed of gelatine and carmine), Dr. Oschafcz of Berlin, 

 tlie 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 l-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 : 



