874 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the jar with the brasswork of the Microscope. On the right a small 

 piece of the foil is fixed to the under surface of the slide, so that this 

 end shall be level with the other. 



Fig. 203 shows a combination of the apparatus with a moist 

 chamber for the examination of blood. In this case the cover-glass 

 has two strips of tin-foil cemented to its under surface, and the drop 

 of blood being spread out in a thin layer between the points is 

 quickly inverted over the ring of the cell. 



The tin-foil slips are kept isolated by the glass slide from the 

 brasswork of the Microscope, and their free ends are clamped to 

 isolated metal supports as shown in fig. 204, and can be connected with 

 a Leyden jar or an induction coil. 



The ends of the wires or slips can also be made to dip into cups 

 of mercury placed on the table, into which the terminal battery wires 

 can also be led. 



Engelmann* also devised an arrangement for electricity (figs. 

 205 and 2(i6) in connection with his gas-chamber. The glass top is 



Fig. 205. 



pierced with two apertures at x x, through which is inserted clay 

 steeped in 1 per cent, salt solution, so as to fill the space between the 



top and the glass plates gg and 7i h 

 (which form a channel for it) and to 

 extend to the sides of the drop sus- 

 i^ V^i C |o. ^ pended from the under surface of the 



' y ' cover-glass, which closes the aperture 



in the chamber. The points of the Du 

 Bois non-polarizable electrodes are placed on x x. 



According to KoUett f it is advisable in using electrical discharges, 

 that the tin-foil points should be 6 mm. apart. The Leyden jar 

 should have a surface 500 sq, cm. and give a spark 1 mm. long. 



Strieker also points out J that the distance of the laminae of tin-foil 

 from one another is of importance in regard to the transmission of 

 the current. As a general rule, they should not be separated from 

 one another to a greater extent than a few millimetres. He prefers 

 to see the two electrodes at the sides of the field, because then the 

 position of the object in regard to them and to the middle line is simul- 

 taneously visible. It is a matter of very great moment to observe 

 and distinguish between the effects of the current in the immediate 

 neighbourhood of the poles and at some distance from them ; for 

 the effects of electrolysis are produced on breaking the current in 

 the vicinity of the electrodes, and the tissues become altered, as 



* Jenaisch. Zeitschr. f. Naturwiss., iv. (1868) pp 331-3, 385 et seq. 

 t Klein, Biirdon-Sanderson, Foster, and Brunton, 'Handbook for the Physio- 

 Icgical Laboratory,' 1873, p. 17. 

 + Op. cit., p. xxi. 



