APPENDIX. 409 



pared by dissolving 3 gm. soluble Berlin blue ( Grubler) in 600 cc. distilled 

 water. A smoothly working syringe of 200-300 cc. capacity, with tightly 

 fitting stop-cock and several appropriate canulae, is the best instrument, since 

 the educated hand of the operator is the surest gauge of the pressure that 

 may be applied with safety. 



A small animal, such as a young rabbit or kitten, is chloroformed and 

 then bled to death by opening the heart or some large vein, so that the ves- 

 sels are emptied as far as possible. It is advisable to undertake at first the 

 injection of a single organ, as the liver, kidney, or lung, rather than of the 

 entire animal. The organ is not removed and is disturbed only as much as 

 may be necessary to expose sufficiently its chief artery. Into this a canula 

 of appropriate size and fitted with a stop-cock is inserted through a small 

 slit and securely tied. In order to avoid the introduction of air, the canula 

 should be filled with the injecting fluid, and the stop-cock turned, before 

 being introduced into the vessel. When the canula is in place and secured, 

 the syringe is filled, fitted to the canula, the stop-cock opened, and the fluid 

 gently forced into the vessels. Great care must be exercised lest sudden 

 and excessive pressure rupture the delicate vessels and the fluid escape. If 

 all goes well, the injected organ soon begins to assume a bluish tint, but 

 until the tissue appears deeply and uniformly colored the capillary injection 

 is incomplete. Before removing the canula, the large vessels should be 

 secured with ligatures. The organ is then removed from the animal and 

 placed in Miiller's fluid or 70 per cent, alcohol for some days before cutting 

 into pieces. Sections of injected organs must not be too thin, but sufficiently 

 thick to include complete capillary loops or networks. In the case of the 

 lungs, after injecting the blood-vessels, the tissue should be moderately dis- 

 tended by forcing the fixing fluid through the air-tubes, which are then 

 ligated. 



It may be repeated, that the purpose of these pages concerning micro- 

 scopical technique is to present a few methods which are satisfactory and 

 thoroughly trustworthy for the majority of histological examinations. The 

 student is urged to persevere with those here given until he has repeatedly 

 carried the manipulations to the successful results which they are capable of 

 yielding. 



