182 



PRACTICAL HISTOLOGY. 



nozzle uppermost while a drop or two of injection is forced 

 out. A few drops are allowed to fall into the stopcock- 

 piece to completely fill it. The two are united, the stop- 

 cock turned, and the injection slowly performed. The 

 piston of the syringe must never be pushed, but always 

 screwed down, to ensure steadiness of pressure. This 

 apparently simple process is very apt to fail because of the 

 difficulty of judging of the amount of pressure applied. 

 If it be too great, capillaries are over-distended or ruptured, 

 and the injection spoilt. This is easily avoided, however, 

 by attaching as is sometimes done a pressure-gauge to 

 the syringe. This is an ordinary mercurial manometer (M) 

 connected to the stopcock-piece of the syringe by an elastic 

 tube containing air, and a stopcock /. When both stop- 

 cocks are open, and the fluid expelled from the syringe, a 

 part of it passes into the elastic tube, compresses the air, 

 and elevates the mercury in the one limb of the manometer 

 above that in the other, and thus indicates the pressure 

 under which the fluid is being driven into the vessels. The 

 syringe, though convenient for rapid injection, is, neverthe- 

 less, tedious; and therefore Ludwig was led to devise a 

 pressure-bottle apparatus. 



340. Pressure-bottles. A simple but efficient apparatus, 



FIG. 61. Pressure-bottle injection apparatus. 



essentially similar to that used by Ludwig for prolonged 

 injections, is shown in Fig. 61. c represents a zinc or 

 copper water-bath with a perforated tray, on which the 



