4
M. A. Asson-Batres
to death, whereas rats provided milk were saved from this fate (Semba 2012). Studies
conducted by Hopkins, Osborne and Mendel, and McCollum and Davis demonstrated
that an unknown, fat-soluble, factor present in milk, eggs, and butter was needed to
sustain long term growth of rats (Hopkins 1912; McCollom and Davis 1913; Osborne
and Mendel 1913).
Like Stepp (Semba 2012), McCollum and Davis (1913) and Osborne and Mendel
(1913) also found that the growth-promoting factor was not a fat, but that “certain
impurities possibly of the nature of a lipoid, might be the active constituent”. Further
work by McCollum and Davis indicated that the factor was not only present in milk
and butter, but was also present in kidney fat, the ether extract of the ripe testicle of
the codfish, and cod liver oil. They speculated that vegetable oils might also contain
the growth-promoting factor. They carried out experiments in which rats were fed
a fat-free diet for 20–25 weeks. At the end of this time, the rats were feeble and
emaciated and had inflamed eyes. When the animals reached this state of deficiency,
the fat-free diet was supplemented 1:1 with cornmeal. McCollum and Davis reported.
“The results were surprising: the rats which received the corn meal addition responded at
once with increase in weight and marked change in appearance…Inflamed eyes which were
evident in many of the animals soon became normal in appearance”. Wheat, rye, and oats
were not as effective as cornmeal in eliciting recovery, and the authors concluded this may
have been due to “quantitative differences in the yield of the unknown accessory substances
under consideration, rather than to an entire absence of the same” (McCollom and Davis
1915).
Several years later, Steenbock wrote in Science that he had completed a considerable amount of work showing that carrots, sweet potatoes, and yellow corn, but not
sugar beets, potatoes, or white corn, had rich stores of the fat-soluble A “dietary
essential” (Steenbock 1919). Taken together, the evidence was beginning to point to
the existence of an essential, lipid-soluble, factor in yellow-pigmented animal and
vegetable fats that was necessary for the growth and well-being of laboratory rats.
The factor was classified Vitamin A as research began to reveal additional, different,
“vital” nutritional factors (Drummond 1920).
Leroy Palmer noted that:
The chemical identification of each of the recognized vitamins as individual substances or
chemical groups is greatly to be desired. As the result of certain studies which I made on the
physiological relation between the yellow carotin and xanthophyll pigments of plants and
the yellow lipochromes of animal tissues and fluids, I became impressed with the fact that
there seemed to be more than a casual relation between the simultaneous presence of the
plant carotinoids and fat-soluble vitamine in butter fat and egg yolk and in the leafy parts
of green plants, and the simultaneous absence of carotinoids and fat-soluble vitamine from
lard (Palmer 1919).
Interestingly, Palmer’s own experiments did not support this view. Palmer raised
50 chickens from hatching to maturity on a carotenoid-free diet and found they
exhibited normal growth and maturation and produced many eggs, although the
yolks of the eggs were essentially colorless due to a lack of carotene or xanthophyll.
Cocks and hens from the carotene-deficient flock produced offspring that appeared
normal except for a complete absence of yellow pigmentation in skin and beaks.
M. A. Asson-Batres
to death, whereas rats provided milk were saved from this fate (Semba 2012). Studies
conducted by Hopkins, Osborne and Mendel, and McCollum and Davis demonstrated
that an unknown, fat-soluble, factor present in milk, eggs, and butter was needed to
sustain long term growth of rats (Hopkins 1912; McCollom and Davis 1913; Osborne
and Mendel 1913).
Like Stepp (Semba 2012), McCollum and Davis (1913) and Osborne and Mendel
(1913) also found that the growth-promoting factor was not a fat, but that “certain
impurities possibly of the nature of a lipoid, might be the active constituent”. Further
work by McCollum and Davis indicated that the factor was not only present in milk
and butter, but was also present in kidney fat, the ether extract of the ripe testicle of
the codfish, and cod liver oil. They speculated that vegetable oils might also contain
the growth-promoting factor. They carried out experiments in which rats were fed
a fat-free diet for 20–25 weeks. At the end of this time, the rats were feeble and
emaciated and had inflamed eyes. When the animals reached this state of deficiency,
the fat-free diet was supplemented 1:1 with cornmeal. McCollum and Davis reported.
“The results were surprising: the rats which received the corn meal addition responded at
once with increase in weight and marked change in appearance…Inflamed eyes which were
evident in many of the animals soon became normal in appearance”. Wheat, rye, and oats
were not as effective as cornmeal in eliciting recovery, and the authors concluded this may
have been due to “quantitative differences in the yield of the unknown accessory substances
under consideration, rather than to an entire absence of the same” (McCollom and Davis
1915).
Several years later, Steenbock wrote in Science that he had completed a considerable amount of work showing that carrots, sweet potatoes, and yellow corn, but not
sugar beets, potatoes, or white corn, had rich stores of the fat-soluble A “dietary
essential” (Steenbock 1919). Taken together, the evidence was beginning to point to
the existence of an essential, lipid-soluble, factor in yellow-pigmented animal and
vegetable fats that was necessary for the growth and well-being of laboratory rats.
The factor was classified Vitamin A as research began to reveal additional, different,
“vital” nutritional factors (Drummond 1920).
Leroy Palmer noted that:
The chemical identification of each of the recognized vitamins as individual substances or
chemical groups is greatly to be desired. As the result of certain studies which I made on the
physiological relation between the yellow carotin and xanthophyll pigments of plants and
the yellow lipochromes of animal tissues and fluids, I became impressed with the fact that
there seemed to be more than a casual relation between the simultaneous presence of the
plant carotinoids and fat-soluble vitamine in butter fat and egg yolk and in the leafy parts
of green plants, and the simultaneous absence of carotinoids and fat-soluble vitamine from
lard (Palmer 1919).
Interestingly, Palmer’s own experiments did not support this view. Palmer raised
50 chickens from hatching to maturity on a carotenoid-free diet and found they
exhibited normal growth and maturation and produced many eggs, although the
yolks of the eggs were essentially colorless due to a lack of carotene or xanthophyll.
Cocks and hens from the carotene-deficient flock produced offspring that appeared
normal except for a complete absence of yellow pigmentation in skin and beaks.