274 THE VITAMINS 



the beginning has presumably become exhausted or depleted. (Not 

 necessarily lost; but "consumed" in that it is needed for, and diluted 

 by, the growth of the animal.) Growth then slackens and usually soon 

 ceases ; often a rather rapid loss of weight begins shortly and the 

 animal goes into a condition of general decline leading to death. 



By the time the body's reserves of vitamin A have been depleted 

 and growth ceases, the animal becomes more susceptible to bacterial 

 infection, and this lowered resistance often shows itself in various ways 

 — most conspicuously in the tendency of a large proportion of such 

 experimental animals to develop a characteristic disease of the eye, 

 variously known as ophthalmia, xerophthalmia, keratomalacia, con- 

 junctivitis, or keratoconjunctivitis. This usually begins with a swelling 

 of the lids of one or both eyes or with indications that the eye is 

 becoming unduly sensitive ; then there commonly develops an inflamed 

 and catarrhal condition of the conjunctivae with a bloody or purulent 

 discharge, the lids becoming scabby or sticky. This, with the swelling 

 of the lids sometimes results in the eye being found completely closed. 

 Often the inflammation extends to the cornea and if not treated may 

 result in permanent blindness, though the animal often dies before 

 the eye disease reaches this stage. The typical extremely severe eye 

 condition undoubtedly involves infection and in this sense is not purely 

 a deficiency disease, yet it is essentially so in its origin, inasmuch as 

 the dietary deficiency so enormously increases the susceptibility of 

 the animal to the infection as practically to determine the incidence 

 of the disease. It is also very significant that without any other treat- 

 ment whatever, the eye disease, if not too far advanced, usually dis- 

 appears quickly when the animal is given any food containing a suffi- 

 cient amount of vitamin A. 



The relation of the diet to this eye disease and its cure was dis- 

 covered by Osborne and Mendel in 1913. At that time they stated 

 that a "type of nutritive deficiency exemplified in a form of infectious 

 disease prevalent in animals inappropriately fed is speedily alleviated 

 by the introduction of butterfat into the experimental rations," and 

 in 1914 they reported "uniform success by substituting cod-liver oil 

 for a portion of the lard in our standard diets. . . . Not only was 

 growth resumed in most cases at a very rapid rate, but all evidence of 

 malnutrition, especially the affection of the eyes, promptly disappeared." 

 Similar cures by feeding materials containing vitamin A have been re- 

 ported repeatedly by Osborne and Mendel and others since that time 

 so that there can be no doubt of the frequent cure of the disease by 

 dietary treatment alone. Moreover, its cure by any other than dietary 



