ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



715 



the dotted lines tlie sockets are not attached to tlie lower plate, but 

 to a disk which rotates with the arm. 



Frog-plate. — The form shown in fig. 140 differs from the frog- 

 plates usually supplied by opticians for observing the circulation in 

 the web of the frog in that it is of ebonite and not of brass, that it is 

 not intended to be laid upon the stage but to stand on its own supports 



Fig. 140. 



just over it, and that it can also be used for the study of the tongue. 

 For the latter purpose half of a ring of cork must be fixed with brass 

 pins round the large aperture, on the side next the end of the plate, 

 and to this cork the cornua of the tongue may be attached. The large 

 aperture is of course to be arranged over that of the stage.* 



Apparatus for Examining the Circulation in the Lung and 

 Mesentery of the Frog. — One of the best objects for observing the 

 capillary circulation is the lung of the frog. The first difficulty in 

 its use is, however, that it is often emptied by the frog and is then 

 useless for observation. On the other hand, when it is swelled up it 

 is so convex that it cannot be covered with a cover-glass, and the use 

 of high powers is prevented. Holmgren, by an ingenious apparatus 

 (figs. 141, 142, and 143), has surmounted these difficulties."}" 



The frog is first immobilized by the subcutaneous injection of 

 curare, and to regulate the state of repletion of the lung, a tube with 

 a tap at the free end (fig. 141) is introduced into the glottis: the 



* Cf. Dr. Klein in ' Handbook for the Physiological Laboratory,' 1873, p. 42 

 (1 fig )• 



t Ranviev's ' Traite technique d'Histologie,' 1878, pp. 600-3 (3 figs.). 



