NON-PROTOPLASMIC CELL CONTENTS 105° 
The result is that the cells elongate more rapidly on the shaded 
side, bending the plants toward the light. It has been recently 
shown that though growth-hormones are produced in the light, 
they function better in the dark. 
26. ViTaMins.—Vitamins are essential food principles for the 
most part manufactured by plants without which animals cannot 
maintain their health. They are designated alphabetically 
as A, Bi, Bs or G, Bs, Bu, Bs, C, D, E, and K and by names 
indicative of the deficiency disease in animals they correct. 
Viramin A, also known as Fat-soluble A, Anti-xerophthalmic, 
and Antt-infective Vitamin, was discovered by McCollom and 
Davis in 1915. It occurs in conspicuous amounts in carrots, 
green leafy vegetables, in a number of fruits, as tomatoes, 
prunes, pineapple and banana, in sweet potatoes, in wheat 
germ, yellow corn meal, whole milk and in cod and halibut liver 
oils. In its chemical and physiological properties, Vitamin A 
is closely related to carotene which occurs in carrots and many 
other plants. Its presence in oils can be detected by the addi- 
tion of a few drops of a chloroform solution of antimony tri- 
chloride to the oil when a blue color appears which deepens 
and then fades. ‘This vitamin protects epithelial tissues against 
bacterial infection, especially that of the respiratory mucosa, 
and is essential to the proper growth of the bodies of young 
animals. Animals deprived of it in their diet lose weight and 
develop a hemorrhagic condition in their eyes known as xero- 
phthalmia. The U.S.P. unit of vitamin A is the amount of 
vitamin contained in 149909 of a grain of the U.S.P. Reference 
Oil taken as a standard. 
VITAMIN B, or Anti-neuritic Vitamin is a water-soluble, thermo- 
labile factor which has been isolated in pure crystalline form 
from rice polishings. Its absence in the diet has been found to 
be the cause of beri-beri, or polyneuritis, a disease of the nervous 
system characterized by muscular incoordination followed by 
paralysis of certain sets of muscles. Its presence in the animal’s 
diet promotes growth by stimulating the metabolic processes, 
protects it from nerve disease and stimulates appetite and 
digestion. It is also essential for normal gestation. This 
vitamin occurs abundantly in yeast, rice polishings and wheat 
