WITH THE MICROSCOPE. 301 



was removed from the carmine solution have elapsed, the preparation 

 is ready for the last preliminary operation. The glycerine used for 

 washing it is poured off, and sufficient strong Price's glycerine added 

 just to cover it. To this, three or four drops of strong acetic acid are 

 added, and well mixed with the glycerine. In this acid fluid the 

 preparation may be left for several days, when a small piece of some 

 vascular part may be cut off, placed in a drop of glycerine, and sub- 

 jected to microscopical examination. If the injected vessels are of 

 a bright blue colour, and the nuclei of the tissues of a bright red, 

 the specimen is ready for minute examination ; but if the blue colour is 

 not distinct, three or four more drops of acetic acid must be added 

 to the glycerine, and the preparation soaked for a few days longer. 



If the nuclei are of a very dark red colour, and appear smooth 

 and homogeneous, more especially if the tissue intervening between 

 them is coloured red, the specimen has been soaked too long in the 

 carmine fluid ; but in this case, although parts upon the surface may 

 be useless for further investigation, the tissues below may have 

 received the proper amount of colour. 



The tissues or organs to be subjected to special investigation 

 may now be removed, and transferred to fresh glycerine ; they 

 may be kept in little corked glass tubes, pi. XXII, fig. 144, and pro- 

 perly labelled. Generally, the tissue will contain sufficient acetic 

 acid, but if this is not the case, one drop more may be added. 



Suppose, now, the nerves with the small vessels and areolar 

 tissue at the posterior and lower part of the abdominal cavity have 

 been placed in one tube, and the prepared tongue of the Hyla in 

 another, the former specimen may be taken out of the glycerine and 

 spread out upon a glass slide. If the specimen be examined 

 with an inch power, numerous microscopic ganglia may be seen, 

 pi. LXVIII, fig. 412. Several of these perhaps are close to small 

 arteries. Those which are most free from pigment cells are selected, 

 and removed carefully by the aid of a sharp knife, fine scissars, 

 forceps, and a needle point. This operation may be effected while 

 the slide is placed upon the stage of the microscope. The trans- 

 mitted light enables the observer to see the minute pieces very dis- 

 tinctly with the unaided eye, if necessary a watchmaker's lens or 

 a three-inch power may be used. The pieces selected are trans- 

 ferred to a few drops of the strongest glycerine placed in a watch 

 glass or in one of the little china colour moulds, 85, p. 47, and 

 left to soak for several hours. 



The microscopical examination of the specimen may now be 

 carried out. One of the small pieces is placed upon a glass slide, 

 in a drop of fresh glycerine, and covered with thin glass. The glass 



