ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 521 



cannot be fully summarized here, and the original must be referred to by 

 those desiring to know the results obtained with the various media. 



Success was obtained with sulphur by special manipulation ; also with 

 piperine, the alkaloid of pepper, and with " biniodide of mercury, solid," 

 which consists of a saturated solution of the biniodide in piperine. The 

 alkaloids of opium, with few exceptions, are all high-class media ; and of 

 the alkaloids generally, the author says " for bacteria mounting, quick 

 work, and splendid definition, giving immensity of light even to the F eye- 

 piece, I am certain they cannot be surpassed, the bacteria being shown 

 like beads of coral when stained with a red dye." Good results were also 

 obtained by holding the prepared cover-glass over the mouth of a vial 

 containing chloro-chromic acid, a highly volatile liquid giving off red fumes 

 when exposed to the air. 



Numerous chlorides and iodides were experimented with, of which we 

 select the following : — 



Chloride of tin is used thus : — " On placing a small portion on the 

 mica slip and subjecting it to heat, dense fumes mixed with the water of 

 crystallization are given off; and when only a clear liquid is left behind, 

 still giving off white fumes. The cover-glass is held in position with a pair 

 of forceps to intercept the fumes, a white deposit is immediately formed, 

 and the moment 'a sufficient quantity is deposited, the cover-glass is with- 

 drawn and held over the heated mica until resublimation takes place, 

 leaving a metallic ' scud ' on the cover-glass. When mounted in piperine, 

 if properly managed, the diatoms will be found lying in a film of chloride 

 of tin, the striae beautifully defined, of a steel-grey lustre, and around the 

 edge of the valve a golden-yellow tinge. The author thinks the definition 

 quite up to the phosphorus mounts. Being a deliquescent salt, it must be 

 mounted when hot, if not, moisture will be again absorbed, and the slide 

 will be found to be worthless when mounted." 



Iodide of arsenic gives splendid definition to the strise, and is also of 

 value for mounting bacteria. 



Iodide and bromide of silver, with a little manipulation, will rival any 

 of the phosphorus and silver mounts. 



Of chloride of tellurium, the author writes, " This preparation, mani- 

 pulated in the same way as the chloride of tin, is the best medium for 

 showing the A. pellncida that I have experimented with. The richness of 

 the colouring is something grand to look at. The beautiful steel-grey 

 striae, bold and well-defined, with the golden-yellow tinged edge of the 

 valve, makes this the most showy slide that can possibly be exhibited, 

 and in my opinion surpasses Professor Smith's American slide, the medium 

 of which has a refractive index of 2 • 4." 



Of chloride of thallium, he says, " This is a very fine medium ; in- 

 stead of the steel-grey a sea-green colour is given to the strise ; with the 

 golden-yellow tinged edge to the valve, it makes a very pretty exliibit. 

 It has a propensity of causing the piperine to crystallize ; this can be got 

 over by using the valerianate of quinine as a substitute for the piperine. 

 I do not think this impairs the resolution, whilst it still keeps up the 

 chromatic appearance. Some of the valves are resolved as well as with 

 the tellurium, others again have got a varnished look, as if the interspaces 

 between the striae were filled up, and after careful examination minute 

 cracks may be seen in the thin film covering the diatom, as if the thallium 

 had infiltrated itself between the cover-glass and diatom. Those valves 

 found in this state are not so well resolved, giving a more faint look to 

 the strise." 



By mixing chloride of thallium and chloride of tin together, and sub- 



1887. 2 M 



