HARDWICKE'S SCIEN CE-GOSSIP. 



173 



THE HOLMAN SIPHON-SLIDE. 



"TTTE have much pleasure in placing before our 

 » » readers an illustration (borrowed from the 

 Monthly Microscopical Journal) of the above re- 

 markable slide. It was first exhibited at the 

 " Microscopical section of the Academy of Natural 

 Sciences" of Philadelphia, by Dr. Joseph G. 

 Richardson, who stated that the apparatus was 

 composed essentially of a strip of plate-glass, of 

 the ordinary length and width (namely, three inches 

 long by one inch wide), but double the usual thick- 

 ness, in the upper surface of which had been ground 

 a shallow groove, elliptical in both its transverse 

 and longitudinal section, and deeper towards one 



use of calcium or electric light to illuminate living 

 specimens is entirely counteracted. When in use 

 it is only necessftry to place the animal (in the case 

 before us a little triton) with some water in the 

 groove of the slide, cover it with a sheet of thin 

 glass, immerse the end of one of the caoutchouc 

 tubes in a jar of water, and then applying the mouth 

 to the extremity of the other rubber-pipe, make 

 sufficient suction to set up a flow of the liquid 

 through the apparatus. The stream of fluid (of 

 course bathing the animal in the cell during its 

 passage) can readily be kept up as in any other 

 siphon for hours or days, and its rapidity exactly 

 regulated by'graduated pressure upon the entrance- 

 pipe, so that in this way a triton may be examined 



Fig. 114. Holman's Siphon, or " Life " slides, showing the means by which circulation of water is carried on. 



extremity. The excavation was so arranged as to 

 receive a small fish, tadpole, or triton, and retain it 

 without, on the one hand, injury from undue 

 pressure, but without, on the other, permitting any 

 troublesome gymnastics beneath the thin glass cover, 

 which, when applied, formed the ceiling of the cell. 

 The great improvement of this slide consisted, how- 

 ever, in the embedding of a small metallic tube 

 (communicating with each extremity of the groove) 

 in either end of the slide, and the adaptation to 

 these two tubes of pieces of slender 'caoutchouc 

 pipe, about eighteen inches in length, one of these 

 being intended for the entrance and the other for 

 the exit of any fluid, cold or hot, which it might be 

 desirable to employ. For examination of larger 

 reptiles, and for demonstrations with the gas 

 microscope, a slide four inches long, with two oval 

 concavities, and a narrow groove more deeply cut 

 for the body of the creature, as shown in the figure, 

 has been devised. With such an apparatus, through 

 which a current of ice-water can be passed, the 

 injurious heating efi"ect which ordinarily attends the 



continuously (as stated by Dr. J. Gibbons Hunt), 

 for a whole week without material injury. 



Among the great advantages of this very in- 

 genious contrivance may be enumerated : first, its 

 security, the animal being prevented from escaping, 

 and the joints of the apparatus being kept tightly 

 closed by the pressure of the atmosphere; second, 

 its portability, the whole preparation, for example, 

 one for showing the circulation of the blood, being 

 made at home, as was done in this instance, carried 

 to a lecture-room in the pocket, and exhibited to an 

 audience hours afterwards ; and third, its con- 

 venience, this arrangement permitting the removal 

 of the slide at any time from the microscope stage, 

 to make way for other experiments, and its instant 

 readjustment when desired. 



Dr. Richardson invited the attention of members 

 to the remarkably clear and distinct view of the 

 circulation displayed by the aid of this apparatus 

 in the caudal extremity of a triton beneath one of 

 the microscopes upon the table, and pointed out as 

 especially worthy of note the marked prominence 



