IN a note which recently appeared in this journal i the writer asserted, on the authority of Freytag, that the refractive indices of the lens and fluid media of the dog's eye are practically identical, and that several other species of infra-primate mammals suffer under the same condition. If this assertion were true, its significance would be very great indeed, since in such case the animals concerning which it is made could not change the focal distance of the eye by any mechanism of accommodation which mammals are known to possess.
At the time my note was published, 1 had been unable to procure a copy of Freytag's original article." My assertion was based on my acceptance of a reference made by an American compiler to Freytag's work, in which a series of values were presented in tabular form as Freytag's. A comparison of the latter with the original article, which I have since obtained, shows that Freytag was incorrectly quoted by his reviewer, although the error is clearly unintentional. Freytag actually gives as mean values of the refractive indices in young and old dogs: for the aqueous humor, 1.3349 ; for the vitreous humor, 1.33483; and for the lens, values ranging between 1.4498 and 1.4666, depending on age. These differences are greater than those obtaining between the refractive indices of the lens and fluid media in the human eye, and are comparable with the differences found in the other mammals which Freytag studied.