BY LR. KLEIN. 121 



Nerves. The rich plexus of non-medullatecl nerve fibres 

 which exists in the adventitia of large bloodvessels, can bo 

 studied in the mesentery of the frog, which for this purple 

 must be prepared in the manner directed in Chapter V. for the 

 demonstration of the nerves of the mesentery. In the same 

 organ it can be shown that the capillaries are also surrounded 

 by non-med dilated nerve fibres. In the nictitating membrane 

 and tongue of the frog, the plexuses which surround the capil- 

 laries may be seen to give out fibrils which enter the walls of 

 the vessels themselves. For this purpose the tongue of the 

 frog must be colored in a half per cent, solution of chloride of 

 gold, and used, after hardening in alcohol, for the preparation 

 of sections. (Sec Chapter XII.) 



The development of bloodvessels will be given in the chapter 

 on Embryology. 

 - 

 SECTION III. MICROSCOPICAL STUDY OF THE CIRCULATION. 



Study of the Circulation in Cold-blooded Animals. 



The parts which may be used for this purpose are (1) the 

 web of the frog's foot, (2) the mesentery of the frog or toad, 

 (3) the tongue of the same animal, (4) the tadpole. 



Web of the Frog. If the animal is not curarized, the 

 arrangement must be employed which was described in Chap- 

 ter III. It is, however, better to employ curare, as described 

 in Chapter XVII. The animal is laid on an oblong plate of 

 glass, on which a cork disk is fixed with sealing-wax, which 

 should be three-tenths of an inch thick, and an inch and a 

 quarter wide. The disk must have a hole in the middle, which 

 should be about three-quarters of an inch wide. At the edge 

 of this aperture pins are stuck, to which ligatures attached to 

 the toes may be secured. 



Mesentery. The preparation of the mesentery is not so 

 simple. A snip is made in the right side of the belly, parallel 

 with the middle line. Before dividing the skin further, it is 

 raised to ascertain where there are no large veins ; the incision 

 is then continued upwards and downwards, in such directions 

 as to avoid bleeding. If, notwithstanding, a vein is divided, 

 the bleeding must be restrained by seizing the end of the in- 

 cision with the clip-forceps. The traces of blood having been 

 removed with filter paper, the muscles are divided in the same 

 vertical line. This having been done, the intestine and mesen- 

 tery are drawn out carefully, and laid on the anterior surface 

 of the belly. The next step is to place the animal on a in Fig. 

 19. (For this, however, a simple glass plate of similar size 

 may be substituted, at the edge of which a cork is fixed, which 

 should have an aperture corresponding to c, covered with a 

 round cover-glass.) The frog having been pushed up against 



