DISOKDEKS IN KELATIOK TO THE EYE 759 



Data of experimental teratology show that peculiarities of temperature, 

 chemical constitution, tonicity, and acidity of nutrient media and fluids 

 may influence the energy and rate of development in normal ova and larval 

 forms, causing an arrest, at a low stage, of definite cells or tissues and of 

 organ anlagen, resulting on the one hand in the loss or non-appearance 

 of certain parts or in the persistence of others which normally disap- 

 pear. The various cleft formations of the eye or its component parts re- 

 sulting in coloboma of lids, iris, or choroid, or nerve-sheaths are ex- 

 amples of the former, while persistence of the canal of Cloquet and of 

 the central hyaloid artery in the vitreous, or of the pupillary membrane 

 represent the latter type of anomaly. The Mongolian fold or epicanthus 

 seen in dyscrinoid idiotism and in some cretins may also be a form of 

 anomalous persistence of a structure which, like the third lid or the nic- 

 titating membrane of lower animals, may have embryonic anlage in man 

 which normally, and usually, retrogresses in fetal life. 



The association of marked developmental defects, amounting even to 

 microphthalmos or anophthalmos, with a rudimentary state of the brain 

 does not necessarily indicate a causal relation. Both conditions may well 

 be coincidental expressions of a common underlying factor. That the 

 normal growth of the eye does not depend on brain development is shown, 

 further, by the fact that normal eyes are often found in anencephalic 

 monsters or in those in which failure of the lateral vesicles to develop 

 normally resulted in a cyclopic brain or nose. 



The influence of the individual glands of internal secretion, on proc- 

 esses of heredity are not fully understood, nor is it known whether definite 

 dyscrinisms are transmitted in the germ-plasma and chromosomes, so 

 that it is not possible to refer this or that ocular malformation or de- 

 velopmental arrest to one or the other endocrin organ. The relation of the 

 endocrin hereditary factors becomes interesting and suggestive in ophthal- 

 mology because of morphological and clinical similarities and analogies 

 between certain disease manifestations on the one hand and individual 

 or racial characteristics of purely physiological significance, on the other. 

 Thus the Mongolian fold or epicanthus, which is a normal heritage of the 

 Chinese child and a stigma of marked constitutional degeneration in a 

 Caucasian, is in both an evident endocrin marking which it is logical to 

 assume is of uniform provenience. Congenital cataracts are frequently of 

 the lamellar form noted as a regular accompaniment of certain definite 

 states of dyscrinism and malnutrition, notably disturbance of calcium 

 metabolism, such as rickets, tetany, and pellagra. Congenital kerato- 

 malacia is almost exactly paralleled by the corneal degeneration seen in 

 animals deprived of the fat-soluble vitamin. Hereditary pigment de- 

 generation of the retina is marked by hemeralopia which is an invariable 

 accompaniment of a series of acquired starvation states, general or specific. 

 Finally, certain congenital ocular dystrophies are associated with somatic 





