42 THE AMERICAN MONTHLY [February, 



jecting spurs, the use of which we shall see presently. A ligature needle 

 should be constructed as follows : Flatten the end of a stout piece of 

 copper wire and having drilled a hole in it, polish the end very smooth, 

 and fix it in a wooden handle. Have ready some fine twine or stout 

 thread ; now insert the nozzle into the left ventricle, having previously 

 filled it with the salt solution. When the tube has passed within the 

 arch of the aorta^ put the ligature needle, threaded, under the vessel; 

 draw the thread through and remove the needle, and tie the tip of the 

 nozzle in the vessel and fasten the ligature to the spurs before men- 

 tioned. This prevents the nozzle from slipping out of position. Now 

 insert the stop-cock belonging to the salt solution into the nozzle, tak- 

 ing care that no air gets between, and turn the cap, when the diminish- 

 ing depth of the solution in the bottle will tell whether it is flowing 

 through the vessels to wash them out. When sufliicient has flowed 

 through, it is only necessary to transfer the stop-cock to the blue injec- 

 tion, when, if all things have gone well, the exposed tissues w^ill almost 

 immediately become colored. This flow may be left uninterrupted for 

 such a time as may be deemed enough to permit the capillary system to 

 be thoi-oughly permeated. This plan answers equally well for the car- 

 mine gelatine injection ; only everything must be kept warm to prevent 

 the gelatine setting. Some prefer this plan to that of the syringe, as 

 the constant renewal of the fluid with this tends to rupture the vessel. 

 Another objection arises from the fatigue to the hand in keeping up a 

 constant and steady pressure during the process. In this plan the noz- 

 zle being fixed once and for all, and without any strain, no such danger 

 as a rupture presents itself, while the steady flow of a five-feet column 

 of fluid is sufficient without hand pressure. There are methods given 

 in books by which insects, mollusca, etc., may be injected. 



A few words in reference to the mounting of injections. The 

 medium for mounting, in most cases, is Canada balsam, and although 

 this is easy of application, it robs an injected preparation of half its 

 beauty, and nearly all of its instructiveness. We see an exquisite net- 

 work of vessels, but look in vain for those important parts which the 

 vessels are there to nourish ; these are blotted out and obliterated by the 

 balsam. The mountant, therefore, should be one which allows the rela- 

 tions of vessels to their immediate substructure to be clearly seen and 

 studied. Such a medium as glycerine solution of varying density 

 should be chosen, that solution being selected which shows these rela- 

 tions the best. The mucous coats of the stomach and intestines, how- 

 ever beautifully and completely injected, lose half their value as in- 

 structive agents when their glandular and villous elements are stamped out. 



\To be continued.^ 



CORRESPONDENCE. 



The lenses of Carl Reichert are making a stir. His former i-i5th 

 now, and truly a i-i2th, oil immersion of 1.25 numerical aperture is in 

 my possession, and in my judgment, as well as that of Dr. Stokes, is a 

 very superior lens. Well corrected, resolves A. pellucida " easily and 

 well" (Stokes) ; long working distance (about i-5oth inch) ; beautiful 

 definition, " wonderful capacity of light " (Stokes). Price, $22 ; with 

 dut}' paid, $35. Qiiality on a plane with Powell, and Leland, and 

 Spencer. — Edward Gray, Benicia, Cal. 



