224< THE RETINA, BY MAX SCHULTZE. 



vided the granular coagulation which occurs soon after death 

 in most of the cellular elements of the retina has not occurred. 

 The isolation of the soft fibres by needles can only be very 

 imperfectly accomplished in the fresh condition and in in- 

 different fluids, but may be effected in retinae macerated in 

 hardening fluids, as, for example, after preservation for some time 

 in iodine serum, and in dilute solutions of chromic acid and 

 of bichromate of potash. The nerve fibres of the retina thus 

 brought into view vary considerably in diameter, many being 

 only just capable of measurement, and therefore under half a 

 micromillimeter, whilst the thickest have a diameter of from 

 three to five micromillimeters. None of them present any 

 traces of attached or imbedded nuclei, and very slight traces 

 of any isolable sheath, or of a differentiation into cortex and 

 medulla. They appear in the form of pale, pliable, very soft 

 fibres, in which no further structure is perceptible than some 

 indication of fibrillation and here and there a cluster of fine 

 granules. All exhibit a great tendency to the formation 

 of fusiform varicosities. In fresh preparations examined in 

 situ, such varicosities however are almost entirely absent, 

 and their formation can be retarded by the application of 

 iodine serum or addition of common salt to serum, but is ac- 

 celerated by dilution of serum with water, and is therefore un- 

 doubtedly a phenomenon of imbibition. The number, size, and 

 form of the varicosities exhibit many varieties, but the appear- 

 ances are always quite different from those presented by the 

 medullated fibres of the brain or spinal cord. In the latter the 

 surface is beset with varicosities, and rendered knotty by the 

 partial escape of the strongly refractile medulla. No trace 

 of such escape is perceptible in the retinal fibres; but the 

 fusiform varicosities they present, correspond to those observed 

 in axis-cylinders from which the medullary sheath has been 

 detached, as may be seen for example in the. fibres of the 

 auditory nerve.* 



That a change occurs in the texture of the optic fibres in the 

 places where varicosities develop, is demonstrated by the fact 

 that the varicosities, especially of the thicker fibres, exhibit 



* M. Schultze's Observationes de retina structura 2>enitiori, 1859, fig. 1. 



