ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 867 



may be introduced into tlie lantern slides prepared from the last 

 negative, wliich also may be retouched if necessary like any other 

 negative. The superiority of such enlargements over negatives made 

 originally of the same size is often very marked. 



Microscopical Electrical Apparatus. — It appears to be but very 

 rarely that in this country any use is made of the electric current in 

 microscopical examinations. We have never seen any apparatus for 

 the purpose in the hands of any English microscopist, and our text- 

 books on the Microscope make no reference to the subject. Nearly 

 all the standard German treatises, however, contain drawings of appa- 

 ratus intended specially for use with the Microscope for observations 

 on the influence of the electric current on blood, living tissues, micro- 

 scopical organisms, &c., and from these and from English text-books 

 on Physiology we have compiled the following summary of the 

 various forms that have been devised. In regard to the utility of 

 such investigations, Dr. Dippel says,* " The use of electric currents 

 is not less important for many microscopical objects than the appli- 

 cation of high temperatures. This physical reagent has in modern 

 times acquired a high (if here and there exaggerated) importance, 

 and scarcely any microscopist who concerns himself with the minute 

 anatomy of plants and animals can afford to neglect its use." 



The simplest apparatus f consists of two needles which can be 

 readily joined to the wires of a battery and with which any given 

 parts of the object can be touched. They can be hooked to be more 

 readily attached. 



PlossVs Discharger X (fig. 193) is simply the ordinary discharger 

 reduced to microscopical dimensions. The conducting wires are con- 



FiG. 193. 



nected with the two platinum wires shown in the figure, the latter 

 being insulated by being inclosed in capillary glass tubes which slide 

 through sprung brass tubes attached to the upright supports by hinge 

 joints, which can bo rotated or set at different inclinations. The 

 object is placed on the glass plato in the centre. The apparatus 

 cannot, however, bo conveniently made available for covered objects 

 on account of the inclination at which the wires must be set, or for 



• Dippel, L., ' Das Mikroskop und Heine Anwendunf?,' 1882, p. 65C. 



t Ko'oin, C, 'Traitd- du Microscope,' 1877, p. G70. See alao Robin's remarks 

 OB the ofTcct of cloctriciU' on the circulation of the blood, &c., ibid., pp. G80-1. 



X Chevalier, A., ' L'Etudiant Micro(,'raphe,' 18G5, pp. 141-2 (1 fi«.). Dippel, 

 op. cit., p. 656 (1 fig.). Harting. I'., ' Das Mikroskop,' 18G6, ii. p. H5, ill. p. 404. 



