162 THE MICROSCOPIST. 



injection. Yet it should not Tbe deferred so long that the ves- 

 sels may become softened, or the injecting material will be ex- 

 travasated. 



To prepare the subject, the principal points to be aimed at 

 are to dissolve the fluids, empty the vessels of them, relax the 

 solids, and prevent the injection from coagulating too soon. 

 For this purpose it is necessary to place the animal, or part to 

 be injected, in warm water, as hot as the operator's hand will 

 bear. This should be kept at nearly the same temperature for 

 some time 'by occasionally adding hot water. The length of 

 time required is in proportion to the size of the part, and the 

 amount of its rigidity. Ruysch (from whom the art of injecting 

 has been called the Ruyschian art) recommends a previous 

 maceration for a day or two in cold water. 



When the size and the subject have both been properly pre- 

 pared, have the injection as hot as the finger can well bear. 

 One of the pipes, G-, Fig. 50, must then be placed in the 

 largest artery of the part, and securely tied. Put the stop- 

 cock, F, into the open end of the pipe, and it is then ready to 

 receive the injection from successive applications of the syringe, 

 A. The injection should be thrown in by a very steady and 

 gentle pressure on the end of the piston-rod. The resistance 

 of the vessels, when nearly full, is often considerable, but it 

 must not be overcome by violent pressure with the syringe. 



If the resistance suddenly ceases or diminishes, it indicates 

 that some vessel is ruptured, and the process must be stopped. 

 If it happens at the commencement of the operation, and the 

 vessel cannot be tied, the injection has failed. 



When as much injection is passed as may be thought advisa- 

 ble, the preparation may be left (with the stop-cock closed in 

 the pipe) for twenty-four hours, when more material may be 

 thrown in. 



The first part of the injecting material forming about a third 



