23 



94. Tonometer devised by C. S. Roy and modified by 

 "W. H. Gaskell. 



Lent by the Government Grant Committee of the Royal 

 Society. '1888. 



The instrument consists essentially of two cylindrical vessels 

 communicating by a tube. The smaller is of brass, and is closed 

 below by a membrane and piston, connected with a light lever 

 whereby the vertical motions of the piston can be inscribed upon 

 a drum, The stopcock at the top admits of this cylinder being 

 filled with oil. The larger cylinder is of glass, and is closed at 

 the top by a tightly fitting vulcanite stopper in which are five 

 holes of exactly the same size into which different pieces of 

 apparatus can be fixed. Usually these are as follows : (1) A 

 cannula some 3 mm. in diameter, which is tied into the venous 

 sinus of the frog's heart under examination ; (2) a smaller cannula, 

 which is inserted into one of the aortic trunks ; by means of 

 these two the heart is fed with an artificial solution of blood ; 

 (3) a metal holder sustaining a piece of cork to which various 

 portions of the apparatus can be attached by pins ; (4) an 

 electrode of peculiar construction ; it is a glass tube " which is 

 hermetically sealed at both ends, and carries within it a pair 

 of platinum electrodes, bent at their extremities into the form 

 of a loop. Two very small holes are blown exactly opposite 

 to each other in the middle of this tube, and the electrodes are 

 fixed within it so that the line joining the two holes is just 

 below the lowest point of the electrodes. Through these holes 

 the vagus nerve can be drawn by a thread attached to its 

 extremity, and by pinning the end of the thread on to the 

 cork" above alluded to the nerve will always remain in con- 

 tact with the electrodes. Since the glass tube is closed above 

 and below the air within it does not escape, and hence, though 

 the cylinder be filled with normal salt solution, the nerve is in 

 the air, and there is no escape of current ; (5) a tightly fitting 

 plug which allows the quantity of fluid in the cylinder to be regu- 

 lated. 



The apparatus was used by Dr. W. H. Gaskell in his experi- 

 ments of the vagus nerve, and a full description of it is given in 

 Phil. Trans. 1882, p. 1019, pi. 70, figs. 22, 23. 



95. Time markers to be used with syphon tubes for 

 recording. Employed by Dr. Gaskell in his researches. 

 See Phil. Trans. 1882. 



Lent ly the Government Grant Committee of the Eoyal 



Society. 1888. 



96. Cardiograph, devised by Marey, for recording the 



movements of the heart. ^ - 



Lent ~by the Biological Laboratory, Eoyal College of 

 Science. ]878. 



