210 LIFE: ITS NATURE AND ORIGIN 



vitamin A, a substance related chemically to carotene and other 

 lipochromes (retinene, astacin) which are functional in the eye 

 region. Thus the Texas State Agricultural Experimental Station 

 reported in 1932 that a Duroc-Jersey gilt on a vitamin A-deficient 

 diet farrowed eleven pigs all without eye-balls. F. Hale repeated 

 the experiment, 04 and one pig was born without any eye-cup at all. 



It is interesting to note that vitamin A (carotene) serves as a 

 prosthetic group in the conjugated protein system serving vision 

 in the higher animals. The equilibrium visual purple (rhodopsin) 

 ^± visual yellow (retinene) ^± visual white concerns the retinal 

 rods, while the visual violet (iodopsin) is involved in the retinal 

 cones useful in night vision and especially important to nocturnal 

 animals, e.g., owls. To prevent "night blindness" aviators wear 

 special red glasses before flying at night, in order to protect their 

 visual cones and render their night vision acute. 



Among cave-dwellers some of the eye deficiencies reported are 

 the following: 



In the salamander Proteus anguineus cornea induction is in- 

 hibited by a thick wad of connective-tissue mesoderm which 

 develops between the eye-cup and the epidermis. In the blind 

 cave-fish Anoptichthys jordani lens induction spontaneously fails. 

 The lizards Amphisbaena and Rhineura lack lens and cornea. 



The blind fishes and blind amphibia form series showing 

 various graded degrees of eye abnormalities, from degeneration 

 of the retina following normal development, to absence of lens, 

 of cornea and of eye-cup differentiation. The caves also have 

 many blind invertebrates, e.g., the shrimp-like crustacean Niph- 

 argus. Reference should here be made to the work of Prof. 

 George H. Parker on neurohumors, and of Prof. Francis B. 

 Sumner on the effects of visual stimuli on the colors of fishes and 

 amphibia. 



These facts raise the question as to what extent deficiencies in 

 foods and in solar radiation (due e.g., to long periods of intense 

 volcanic activity, as in the upper Cretaceous), may result in 

 abnormalities under natural conditions. Thus J. Alexander 

 stated: 65 "The riddles presented by the disappearance of various 

 animal species and human tribes are, of course, open to many 

 possible interpretations — change of climate, pestilence, extermina- 

 tion or submergence by other animals or tribes. A more subtle 

 but equally potent possibility is food failure — not necessarily 

 actual famine, but a deficiency in the supply of certain foods 



