INJECTIONS OF VEINS, ETC. 701 



" A small portion of intestine can be injected by cutting out 

 the corresponding portion of mesentery attached to it ; and after 

 searching for a large vessel, all the others may be tied, together 

 with the open ends of the alimentary tube." " A pipe of some- 

 what smaller diameter than the vessel should be selected, and an 

 opening may then be made in the vessel of sufficient size to 

 admit the pipe, which can now be inserted. The needle, charged 

 with thread or silk, is then carefully passed round the vessel, the 

 thread seized with forceps, and the needle withdrawn over the 

 thread. This operation is sufficiently simple where the vessel is 

 large and strong ; but where thin and easily torn, it requires great 

 care. The thread is now tied tightly round the vessel close to 

 the extremity of the pipe, and then attached to the two projecting 

 wires, to prevent the possibility of slipping. 



"In injecting from veins a similar method is pursued, taking 

 care to choose a vein in which the valves are not numerous, or 

 in which they are altogether absent. The portal vein can be 

 reached by opening the abdominal cavity, care being taken not 

 to tear any of the branches below the point where the pipe is 

 inserted. 



" Greater care is required to fix the pipe in the vessels of fish, 

 in consequence of their being so readily torn. Excellent injec- 

 tions of fish may frequently be made as follows : The tail is cut 

 off with a sharp knife at a short distance posterior to the anus, 

 and if the cut surface be examined the ventral artery may be 

 easily found situated immediately beneath the bodies of the ver- 

 tebrae. A pipe is carefully introduced and pushed down some 

 distance, so as to prevent the injection from coming out, or the 

 end of the vessel may sometimes be separated from the surround- 

 ing parts and tied in the usual way. By this simple proceeding 

 capital injections can often be made very easily. 



"Minute injections of the branchiae of some of the mollusca 

 may often be made by very carefully placing the pipe in the 

 largest vessel that can be found, and slowly injecting. The ex- 

 treme delicacy of the vessels prevents any attempt being made 

 to tie them to the pipe, and, of course, much injection will be 

 lost. From the large size of the vessels, however, much will run 

 into the capillaries. In this way I have easily succeeded in in- 

 jecting the branchiae of the Pinna ingens, and fresh-water mussel 

 (Anodon), both of which form beautiful microscopical objects. 



"In order to inject the smaller gasteropods (slugs, snails, &e.), 

 we must pursue a different method. In the muscular foot of 

 these are situated many large lacunae, or cavities, which commu- 

 nicate with the vascular system, or, in fact, form the vessels 

 which are distributed to this organ. If the injection can be 

 forced into any of these lacunae, it may be made to traverse the 

 whole vascular system. To introduce the pipe a small hole is 

 made obliquely in the foot, taking care not to force the instru- 

 ment too far. A small pipe is next inserted, and when the pre- 



