BIOLOGICAL SIGNIFICANCE OF VITAMINS 



mally when the fats of the diet consisted largely of butterfat but failed 

 when certain vegetable oils devoid of vitamin A were used; this ob- 

 servation was especially significant at a time when Danish children 

 given skim milk plus vegetable fats were developing the same symptoms 

 as those observed in rats. (3) Chicks grew normally if allowed access 

 to sunlight shortly after hatching, but developed severe leg weakness 

 when hatched early in the spring; at that lime attempts were being 

 made to start the chicks during the winter months so tliat broilers 

 would be available when the demand was heavy. When the de- 

 ficiency agent was found to be vitamin D, not only was the poultry 

 industry saved but a program was initiated which led to the eradication 

 of human rickets. 



By 1925, many laboratories were undertaking systematic 

 nutritional studies, and further attempts were being made to produce 

 specific beriberi in rats and chicks, vitamin A deficiency in rats and 

 dogs, vitamin C deficiency in guinea pigs and monkeys, vitamin D 

 deficiency in chicks, dogs and rats, and pellagra in dogs. Rough assay 

 procedures were developed; foods richest in each of these vitamins 

 were designated "protective" foods. Theoretically, this knowledge was 

 all that was needed to prevent the deficiency disease resulting from the 

 lack of each respective vitamin. Carlson, a few years ago, stated that 

 we had sufficient knowledge to prevent all beriberi in the world long 

 before vitamin Bi was synthesized, a statement which is true in a limited 

 sense. Thus, Chamberlain and Vedder reduced the incidence of beri- 

 beri in the Philippine Scouts by issuing unpolished rice, but the prob- 

 lems of producing high-quality unpolished rice and of educating 

 people to use this type of rice product as part of their diet are still with us. 



All these studies were most intriguing to ever-increasing numbers 

 of research workers. The bars were now down to the progress of nutri- 

 tion research and the studies gained momentum each year. 



Some wanted to know what happened during each deficiency 

 and how the vitamin functioned in producing normal animals. One 

 of the first attempts involved histological studies of tissues from vitamin- 

 deficient animals; and it was soon recognized that the absence of a 

 minute trace of a nutrient led to extensive structural changes in certain 

 tissues. Even greater progress was made when the function of vita- 

 mins was related to the dynamics of the living cell. In 1921, Seidell 

 stated that, aside from a possible significant diff'crcnce in the degree of 



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