An elementary compendium of physiology; for the use of students / By F. Magendie ; Translated from the French, with copious notes, tables and illustrations by E. Milligan.

  • Magendie, François, 1783-1855. Précis élémentaire de physiologie. English
Date:
1826
Catalogue details

Licence: Public Domain Mark

Credit: An elementary compendium of physiology; for the use of students / By F. Magendie ; Translated from the French, with copious notes, tables and illustrations by E. Milligan. Source: Wellcome Collection.

    92/668 (page 56)
    Modification of vision by the different ages. Vision in the different ages. Tlie eye is very early formed in the foetus. In the embryo, the eyes appear in the form of two little black points. At the age of seven months, they are capable of modi¬ fying the light, so as to form an image on the retina, as we have ascertained by experiment. Before this period, the eyes could not be of such use, since the pupil is shut by the pupillary membrane.* At seven months this membrane disappears: it is generally said that it bursts ; probably it is absorbed. This is also the period of the Viahilite^ or confirmed vitality of the foetus. Foetuses have been found, however, at six, and even at five months, the eyes of which presented no trace of this membrane. The eye of a child, and that of an adult, are not quite the same: but their difference is not remarkable. In the first, the sclerotic is thinner, and even slightly transparent; the choroid is reddish on the outside, and the dark shade of the internal surface is less deep ; the retina has a greater proportional developement; the aqueous humour is more abundant, which gives a greater projection to the cornea; the crystalline has also much less consistence than in the adult. The eyes are, before birth, closed, and, as it were, fixed together. In certain animals, they are joined by the palpebral conjunctiva^ which passes from the one to the other, and which does not break until after birth. From youth to manhood the quantity of the humours of the eye diminish insensibly; they afterwaixls diminish in a more evi¬ dent degree : This diminution is more particularly manifest in old age. * According to ]\I. Edwards, the pupillary membrane is formed by the pro¬ longation of the membrane of the aqueous humour, and of the external layer of the choroid. He denies that any water is found in the anterior chamber before the rupture of this membrane; and proves that, previously, it is all accumulated in the posterior chamber; 1 st, because the membrane so named is not its secre¬ tory organ ; 2d, because it exists in the posterior chamber ; 3d, because, before the seventh month, the same membrane of the aqueous humour is a shut sac, presenting all the characters of a serous membrane.