300 THE VITAMINS 



liberating vitamin A for growth but not for curing ophthalmia, and 

 concluded, after a critical examination of Hume's original data, that 

 growth in Hume's animals ceased because of an insufficiency of the 

 antirachitic vitamin as distinguished from vitamin A. When its defi- 

 ciency was compensated for by radiation, growth was restored and 

 continued until vitamin A was exhausted ; then ophthalmia made its 

 appearance and rapid failure supervened. Their theory postulated that 

 the antiophthalmic and antirachitic properties are resident in distinct 

 entities, as proposed by McCoUum, Simmonds, Becker and Shipley, and 

 attempted to explain the variable results obtained by different investi- 

 gators on the basis of variation in the relative amounts of vitamin A 

 and antirachitic vitamin stored in the body of the experimental animal. 

 Regarding their own experiments, they said, "Young rats raised on 

 our stock ration" (poor in the antirachitic factor as compared with 

 its content of vitamin A) "and transferred to a purified ration carrying 

 yeast as its only source of vitamins, will grow for a few weeks then 

 cease growing completely or partially and ultimately will fail due to 

 the incidence of ophthalmia or infections of the respiratory tract. 

 Aerated cod liver oil or light from a quartz mercury-vapor lamp, both 

 well known as antirachitic agents will eliminate the initial failure of 

 growth or when prevalent, will restore it without appreciably post- 

 poning the final failure due to ophthalmia or respiratory diseases." They 

 also found that after the incidence of ophthalmia irradiation of animals 

 did not promote growth. Evidently both vitamin A and vitamin D 

 are necessary for growth. 



Occasionally experiments may be complicated by the fact that ultra- 

 violet light has a deleterious efiFect on the eyes. Goldblatt and Moritz 

 (1926) reported that "Direct irradiation induces a conjunctivitis and 

 opacity of the cornea which complicates other eye changes induced by 

 the diet, and also probably affects the general condition of the animal." 



Thus while it is now generally accepted that light is not the equiva- 

 lent of vitamin A, yet in view of the fact that direct irradiation of the 

 animal body by sunlight or ultra-violet light may introduce variables, 

 it is considered good technique to provide vitamin D in vitamin A ex- 

 periments by a method other than direct irradiation of the animal body. 



Production of Vitamin D by Irradiation 



Working independently, Hess and Steenbock reported almost simul- 

 taneously the possibility of conferring antirachitic potency on food ma- 

 terials by irradiating them with ultra-violet light.* 



• According to a recent note in the Journal of the American Medical Association, the first 

 public announcement was by Hess in June 1924, which appeared in print in October 1924; 

 while Steenbock's original announcement appeared in September 1924. 



