i^TS Dr. Barry's Account of the Discoveries of Keber 



expect in a glass of its focal length, with its large aperture (of 

 from 100 to 110 degrees, according to the absence or the thick- 

 ness of a medium covering the object)/' My microscope has a 

 " slow motion " for fine adjustment of focus, given by a nut that 

 has its margin divided into tenths *. 



Keber insists on the absolute necessity of obtaining for exa- 

 mination particles that are exceedingly minute. He conceived 

 the beautiful idea of first dispensing with art in getting these, 

 and collecting such as are " weathered '' off — particles of Nature's 

 own preparing. Not until these had been well studied did he 

 venture to examine the detritus artificially obtained, and of this, 

 too, he always selected the minutest. Nothing could be truer 

 than what Keber says on this subject of minuteness. It alone 

 would have been a boon to physiology. I tried his plan, exa- 

 mined particles '' weathered " off, — compared these with the 

 minutest of such as had been obtained artificially,— saw the same 

 in both, — and am therefore enabled to confii*m his statement that 

 the appearances described by him are not the product of arti- 

 ficial dislocation. 



He points out where it is important to avoid adding water, 

 and where to add or not to add a covering of glass. Here, too, 

 my own experience enables me to attest the advantage of rigor- 

 ously attending to what Keber recommends. 



Most aptly does he describe the fine scrapings of the roots 

 of plants, after evaporation has proceeded for a while, as appear- 

 ing '' compose.d of a network of variously twisted and over- 

 lapping filaments and scales, leaflets and granules ; and in fact 

 -as everywhere presenting a composition like that of sponge." 

 " A system of communicating hollows, interstices, or passages," 

 as Keber describes what he saw in the detritus of scraped, dry, 

 organic objects, no careful observer can, I think, deny. Such 

 a composition of scales that overlap each other, and fibres that 

 run in all directions, cannot but resemble sponge. 



The scales, however, met with among the weathered-off par- 

 ticles, as well as those found when the detritus has been ob- 

 tained, by scraping or by tapping, in its minutest form, require 

 an additional remark. Each of these scales I find to be a flat or 

 discoid nucleus that has divided into many still adherent parts, 

 which are pressed into various forms, each part being itself a 

 nucleus, and having its single nucleolus. The round orifices of 

 Keber, I think, must be the nucleoli now referred to. 



In animal and vegetable formations, look where you will, you 



♦ It is known that the best performance of an object-glass of such an 

 aperture as that in question is thus obtained hy measuring the thickness of 

 the medium covering the object, and setting the collar of the object-glass 

 accordingly. 



