300 HOW TO WORK 



the artery. This part of the operation is conducted as fully 

 described in page 98, except that the Prussian blue fluid given in 

 p. 296. is used instead of the more inexpensive fluid made with 

 common glycerine. The injection ought to be complete in from 

 twenty minutes to half an hour, and sometimes in less time than 

 this. The injection being pale, cannot be very distinctly seen by 

 the unaided eye, but if the operation has been conducted success- 

 fully, the tissues will be found swollen and the areolar tissue about 

 the neck will be fully distended. The observer must not, however, 

 attempt to inject a Hyla before he has succeeded in injecting the 

 common frog perfectly, for the Hyla, being smaller, is somewhat more 

 difficult to inject than the common frog or the newt. 



The injection being complete, the abdominal cavity of the frog 

 is opened, and the viscera washed with strong glycerine. The legs 

 may be removed, the mouth slit open upon one side, and the 

 pharynx well washed with glycerine. If it is desired to prepare one 

 organ only, this may, of course, be removed and operated upon 

 separately ; but I generally subject the entire trunk, with all the 

 viscera, to the action of the carmine fluid. If the brain and spinal 

 cord are special objects of enquiry, the cranium and the spinal 

 canal must be opened so as to expose the organs completely, before 

 the staining process is commenced. It is, however, better to adopt 

 the process described in p. 304, and in investigations upon the brain 

 and cord. 



Enough of the carmine solution is next placed in a little porcelain 

 basin or gallypot, to cover the entire trunk and viscera. The speci- 

 men is then moved about in the carmine fluid, so that every part 

 that is exposed is thoroughly wetted by it ; sometimes slight pressure 

 with the finger facilitates the imbibing process. It is left in the 

 carmine fluid for a period varying from four to six or eight hours, 

 being occasionally pressed and moved about during this time, so as 

 to ensure the carmine fluid coming into contact with every part. 

 By this time the blue colour of the vessels of the lungs, viscera, &c., 

 will have entirely disappeared, and all the tissues will appear uni- 

 formly red. The staining is now complete. The carmine fluid is 

 poured off and thrown away, and the preparation washed quickly with 

 the glycerine solution, p. 296. This fluid may be preserved in a wash 

 bottle, made according to the plan figured in pi. XXII, fig. 143, but 

 smaller than this, and projected upon every part so as to wash away 

 the superfluous carmine fluid, pi. LVI, fig. 342. The specimen is now 

 placed in another little basin and some strong glycerine poured over 

 it ; it is then left for two or three hours, and a little more strong 

 glycerine added ; when, from six to twelve hours since the specimen 



