Literary Notices. Ixxvii 



matic cones. Concerning the fact discovered by Mrs. Ladd-Franklin 

 and Dr. Ebbinghaus that white produced by union of different colors 

 varies in intensity when the illumination varies, Kries says : The simi- 

 larity of intensity prevailing for high intensities becomes altered on di- 

 minishing the intensity according to the rule that the mixture which has 

 the greatest "rod-valence" then has overplus of colorless light. He 

 really interprets Hering's white-valence as rod-valence and offers a val- 

 uable contribution to the physiologico-anatomical construction of color 

 vision. The position lies between that of Helmholtz and Hering. 

 The paper is too extended to be abstracted here and all interested 

 should read the original. c. L. h. 



The Optical Properties of the Medullary Sheath.^ 



This paper is chiefly significant because it illustrates a method of 

 investigation which is as yet but little known. A study of the optical 

 properties of medullated and non-medullated nerves shows that in po- 

 larized light with crossed Nicols and a gypsum plate interposed the med- 

 ullated nerves transmit red, orange or yellow light, while the non-med- 

 ullated nerves transmit violet, indigo or blue. The acuracy of this 

 conclusion was checked by control preparations stained by the Weigert 

 and the osmic acid methods. As applied to the optic nerve it appears 

 that in animals born blind ( rabbits ) the nerves remain non-medullated 

 until the eyes are open. The various sensory and motor nerves, asso- 

 ciational tracts etc. show color differences at any given embryonic stage 

 which enable one to judge of the extent of medullation and thus of the 

 order in which they acquire their sheaths. 



C. J. H. 



The "Cajal's Cells" of the Human Cortex. ^ 



In this contribution Dr. Retzius completes our knowledge of cer- 

 tain peculiar cells found in the so-called molecular layer of the cerebral 

 cortex. These cells have been previously described by Cajal and Ret- 

 zius in the rabbit, mouse, rat, and cat. This knowledge is now sup- 

 plemented by a very exhaustive treatment of their structure in the hu- 

 man brain. Their development history has been worked out in a full 



1 Ambronn, H. and Held, H. Ueber Entwickelung und Bedeutung des 

 Nervenmarks. Berichte Verh. kl. Sachs. Ges. Wiss, zu Leipzig. Math.-Phys. 

 Classe. 1895, I. 



^Retzius, Gustaf. Weitere Beitrage zur Kenntniss der Cajal'schen 

 Zellen der Grosshirnrinde des Menschen. 6 plates. Biologische Untersuchungen. 

 N. F., VI, 2-3, 1894. 



