Ixxvi Journal of Comparative Neurology. 



onstration by Fish, Herrick and others and subsequently by G. Elliot 

 Smith that these fibres are olfactory tracts, putting the olfactory lobes and 

 the hippocampus in direct connection. Though this tract is so much re- 

 duced in man, yet its appearance cotemporaneously with the olfactory 

 connections is a strong corroboration of the homology. 



c. J. H. 



Functions of the Retinal Bods. 



Heringi has recently made several contributions to the so-called 

 Purkinje's Phenomenon. When a red and a blue surface (whether the 

 color be inherent or spectral) appear equally saturated and then the il- 

 lumination is diminished the red becomes fainter and finally disappears. 

 The same is true of yellow and green. The change is shown by ex- 

 periment to reside in the eye which during accommodation to darkness 

 becomes more sensitive to blue-green and less so to red-yellow. Even 

 if the colors are unaltered and the general field is darkened the result 

 is produced. The gradual disappearance of the colored components 

 as against the colorless is the essence of the Purkinje phenomenon. 

 The sensitiveness to white increases and to color decreases from the 

 fovea toward the periphery of the retina. In the macula lutea the 

 color sense alone prevails. Hering explains these phenomena on the 

 basis of the different degrees of saturation with white of different col- 

 ors and his familiar theory of color vision. Kries,^ however, gives a 

 much more complete and satisfactory discussion of the matter. 



He shows first that if the illuminated spots are so small that their 

 image falls within the macula the change in intensity is not produced 

 by accommodation to darkness so long as fixation continues, i. e. so 

 long as the image remains in the fovea where as we know only cones 

 are found. By exclusion it is easily concluded that the rods alone are 

 responsible for Purkinje's phenomenon. The rods then are character- 

 ized by (i) total color blindness, producing the sensation of colorless 

 light only whatever the wave length, (2) by greater excitability to short 

 and medium wave lengths, and (3) by a great adaptability to various 

 intensities. 



These conclusions stand in interesting harmony with those of M. 

 Schultze {Arch. f. mik. Anat. II, 1866,) who showed that nocturnal ani- 

 mals and birds lack the cones. The sensation of white may, therefore, 

 be produced either by the rods or by a suitable excitation of the trichro- 



iPfliiger's Archiv. LX, p. 1,19, and LXI, p. 106. 



'Ueber die Funktion der Netzhautstabchen. Zeitschrift f. Psych. IX, 2. 



