GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. XXXV 



allowed to work as long as the injection will last. The mer- 

 curial apparatus of Hering is well adapted for the expulsion 

 of atmospheric air. If this is not to be obtained, I apply the 

 jet of the waterpipe on the same principle. The atmospheric 

 pressure of the apparatus is measured by means of a mano- 

 meter, and the rapidity with which the injection is forced 

 onward can be regulated by retarding or accelerating the 

 entrance of the mercury or water. 



When the blood-vessels are to be injected, the canula must 

 in all instances be introduced and fastened into the vessel ; 

 but, in the case of lymph-vessels, according to Ludwig, the 

 canula need only be stuck into the tissue, and firmly tied to it. 



The point of the canula should be cut like a pen, and there 

 should be a groove behind the aperture to prevent the ligature 

 from slipping. In the injection of blood-vessels, all means of 

 escape should be stopped, with the exception of one; and when 

 the fluid flows freely from that, no more fluid should be in- 

 jected. The injecting fluid distributes itself gradually through 

 all parts, if the pressure be steadily maintained. Even though 

 it is discharged to some extent at one point, injections with 

 solutions of silver should be kept up for at least half an hour, 

 under very gentle pressure ; and, in this case, it is not requi- 

 site to tie any vessels when the injection is completed. It is 

 only requisite to throw the tissue into dilute alcohol, in order 

 to preserve it perfectly. When it is only required to show the 

 blood-vessels, and not the parietes of the vessels, coloured fluids 

 should be employed ; and if the arteries and veins are to be 

 distinguished, each system must be separately injected with a 

 fluid, which must not traverse the capillaries. The material 

 in which the colouring matter is suspended is usually wax, 

 and the colouring substance some granular pigment, as ver- 

 milion, red lead, etc. The injection can only be satisfactorily 

 made with a warm syringe and warm tissues, as otherwise it 

 cools too rapidly. After an injection of this kind has been 

 made, the structure of the tissues can no longer be investi- 

 gated. We can only discern one or more layers formed by the 

 ramification of the vessels, and of course the object can only 

 be examined by direct light. Injections thus made are also 

 used for the so-called corrosion preparations. In the produc- 



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