HISTOLOGICAL METHODS. 183 



animal or organ is laid, and covered with glass (g). The 

 water is warmed by an ordinary Bunsen's burner, and its 

 temperature is indicated by a thermometer (/). Two Wolff's 

 bottles (B) one containing, say a carmine mass for inject- 

 ing arteries, and the other a Prussian blue mass for veins 

 stand in the water, so that when a hot injection has to be 

 made, the mass may be readily warmed. The masses are 

 expelled from them by air driven from a large Wolff's bottle 

 A, by water flowing into it from a tap (w\ The pressure 

 exerted upon the air in A is indicated by a mercurial 

 manometer M, and its amount, of course, depends upon 

 the rapidity with which the water is allowed to flow. Glass 

 nozzles, each with a small shoulder, as in n, Fig. 60, for 

 securing them in the vessels, are tied in the indiarubber 

 tubes from the injection-bottles (B); and when one or other 

 injection is not required, it is cut off by the stopcock of its 

 exit tube (c). The corks of the bottles are of vulcanised 

 indiarubber. The lengths of the glass tubes penetrating 

 them are indicated in the Fig. The elastic tubing requires 

 to be very carefully tied over the glass to prevent leakage. 

 Such an apparatus is of great service, for its action is 

 automatic, and the pressure can be very finely graduated. 



341. Injection. The blood-vessels should be injected 

 immediately after death from chloroform. When the 

 breathing is just about to cease the right auricle should be 

 opened to allow the vessels to empty. Previous to injection 

 the vessels may be washed out with a stream of f per cent 

 salt solution, heated to 40 C. if the animal be warm-blooded. 

 The use of the salt solution, however, is not essential. 



If a gelatine injection be used, it must of necessity be 

 heated to about 40 C., and the animal must also be kept 

 warm ; but even when an injection that is fluid at ordinary 

 temperatures is employed, it sh'ould be heated 40 C. or so, 

 because of the vascular spasm which a cold fluid is apt to 

 occasion. 



It is very important always to begin with a low pressure, 

 say J an inch of mercury, and to increase it very gradually 

 to 3 or even to 4 inches. When the injection is complete 

 the artery and vein are ligatured, and the organ placed 



