624 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



old brass plates is retained, but in place of brass glass is used, the 

 edges of wbich are serrated for the string. The brass pin is at 



present only cemented to the plate ; it would be better if it passed 

 through it. 



Groves and Cash's Frog-trough for Microscopical and Physio- 

 logical Observations. — Some years since Mr. J. W. Groves devised a 

 simple guttapercha trough, in which circulation in the webs of frogs 

 could be observed for a considerable time without the web becoming 

 dry. This was effected by keeping the feet of the frog entirely 

 covered with water, into which the objective (protected by a water- 

 tight cap closed below by a piece of thin glass) could be lowered 

 after the fashion of Mr. Stephenson's submersion objective. This 

 contrivance he and Dr. Theodore Cash have considerably improved. 

 The trough (fig. 105) is long enough to admit a full-sized frog ; in 



Fig. 105. 



the bottom, which is lined with cork, are two windows of glass, through 

 which light may be transmitted to the webs of the feet. At the 

 anterior end is a projection, with a cork bottom and glass window for 

 the examination of the tongue, and another similar projection at the 

 side for the observation of the mesentery or lungs. The trough is 

 made of vulcanite, and is watertight, but at the posterior end is a 

 sliding piece by which that end can be opened and a thread passed 

 through to the lever of a myograph. In convenient situations are 

 binding screws for the connection of wires from a coil or battery. 



