XXXIV INTRODUCTION. 



described in the several chapters devoted to the consideration 

 of each. The results obtained depend very much on the mea- 

 sures adopted, though it was thought it would prove of advan- 

 tage to give here a general account of them. 



Besides the mode of staining the tissues effected by dipping 

 them in various solutions, another may be mentioned in which 

 coloured fluids are injected into the vessels. Formerly injec- 

 tions were only made with the object of rendering the lymph 

 or blood-vessels visible by means of coloured material, and the 

 structure of the vascular walls was wholly disregarded ; but 

 in the present day injections are made with the object of ex- 

 hibiting the structure of the parietes of the vessels. For this 

 purpose, for example, a solution of nitrate of silver may be 

 injected. Where, however, a solution of this kind is employed, 

 the tube which is introduced into the vessel, and termed the 

 canula, must be made of glass or platinum, and be connected 

 with the syringe, which should be constructed of the same 

 material, by means of an india-rubber tube. 



Instead of the syringe, an apparatus may be applied in 

 which the injection fluid is propelled by the pressure of air. 

 This mode of injecting, first introduced into practice by 

 Ludwig, is far more certain and elegant than the old method 

 of the syringe. The injection fluid is, once for all, placed in a 

 Woulf 's flask, the size of which is appropriate to the quantity of 

 fluid required to be used. Into one neck of the flask a tube 

 is inserted air-tight, and reaching to the bottom, the upper 

 extremity of which is bent at a right angle, and drawn out into 

 a point : the other neck of the flask is surmounted with a 

 short and also rectangularly bent tube. When this is connected 

 with an apparatus from which air can be driven under a defi- 

 nite pressure, the injecting fluid must be expelled from the 

 opposite tube. If, now, a canula connected with a short india- 

 rubber tube has been fastened into a blood-vessel, and has 

 been subsequently filled with an indifferent fluid by means of 

 a pointed glass tubule, the apparatus can be at once put into 

 action ; and when it is seen that the injecting fluid begins to 

 be discharged at the pointed extremity of the tube connected 

 with the Woulf s flask, that point is quickly introduced into 

 the india-rubber tube of the canula, and the apparatus is 



