

GENERAL METHODS OF INVESTIGATION, BY S. ST11ICKER. xxiii 



development of gas occurs, that but little confidence can be 

 placed in the results that are observed to follow their passage. 

 The amount of electrolysis that occurs with induction currents 

 is much smaller, and they have therefore been most generally 

 employed. The arrangement in which there is a single shock 

 on opening and closure of the current is particularly advan- 

 tageous. The shocks obtained from a Ley den jar are infinitely 

 superior to the constant currents, because the instantaneity 

 of the shock causes the disturbing influence of the evolu- 

 tion of gas bubbles to be altogether abolished. 



It is not practicable to carry out the examination of tissues, 

 under the influence of electrical currents, with the same 

 elegance of detail as can be accomplished when a simple slide 

 only is employed. The single circumstance that the tin-foil, in 

 adhering to the glass, makes the surface irregular and uneven, 

 renders it necessary that the sections of the preparation should 

 be thicker, and proportionately interferes with the investiga- 

 tion by means of high powers. I endeavour, therefore, to 

 combine my researches with electrical currents, with those 

 conducted in the gas cell. By this means I am able to avoid 

 the inconvenience alluded to : for if the cavity of a slide, 

 adapted as described above for a gas cell, be surrounded by a 

 layer of soft cement, it is quite possible to place the electrodes 

 in close proximity with the preparation which is on the inner 

 side of the cover, and to examine it in consequence with high 

 powers, I attach to each side of the slide a strip of tin-foil 



Fig. xi. 



which passes over the putty, and reaches its inner side (s s, 

 fig. xi.) Cemented to the cover are also two small strips of 

 tin-foil (fig. xi., s s'), which, running in the axis of the cover, 

 leave between them a space of a few millimeters in diameter. 

 The object is placed at this spot, and the cover is so disposed 

 on the wall of putty that the metallic strips of the cover lie on 

 the strips covering the putty, and the cover is then firmly pressed 



