The microscope and microscopical technology : a text-book for physicians and students / by Heinrich Frey ; translated and edited by George R. Cutter.

Date:
1880
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Licence: Public Domain Mark

Credit: The microscope and microscopical technology : a text-book for physicians and students / by Heinrich Frey ; translated and edited by George R. Cutter. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    but which has been recently more accurately recognized and studied. On the fresh rod it is seldom that anything of it can be seen, only examinations with oblique light and a rotary stage show us a trace of the same, if one of the strongest im- mersion systems can be used. It becomes distinct only when distending reagents are resorted to, as, for example, dilute serum to which a little acetic acid may be added, dilute nitric acid, etc. Osmic acid (1-2 per cent.) also affords good prepa- rations and, with careful picking in water, presents transverse sections of these plates. The same foliaceous disintegration also occurs on the outer portions of the cone-rods (figs. 382, 383, 2, a). Finally, M. Schultze (we have thus far quoted from his works) found an infinitely delicate longitudinal fibrillary struc- ture covering the rods and cones externally throughout their entire length (fig. 383). One may think of the primitive fibril- lse of the axis-cylinders and ascribe the latter signification to the rod- and cone-fibres. Still the connective-tissue nature of this external striation is undoubted. It belongs to a very deli- cate envelope which is connected with the limitans externa. More recently the indefatigable investigator, now deceased, discovered in the interior of the inner members of the cones and rods a very fine filamentous apparatus. The latter is possibly of a nervous nature, and corresponds to the primitive fibrillse of the axis-cylinder formerly looked for on the outer sur- face. For this purpose, also, osmic acid constitutes the best ac- cessory. The macula lutea and fovea centralis require no new methods. Their structure must be ascertained from the text-books on histology. The usual hardening treatment with chromic acid and chro- mate of potash (and alcohol) also serves to show the relation of the blood-vessels to the retinal layers, and their advancement to near the intergranular layer ; while the delicate vascular net-work in its extension (fig. 384) (for the demonstration of which we recommend the injection of the eye of the ox and the sheep) requires surface views. With regard to the pathological changes of the retina, we are at present acquainted with hypertrophies of the connective- tissue parts, with a corresponding degeneration of the nervous