438 DISEASE IN WILD MAMMALS AND BIRDS 
and reserve alkalinity. A diet with a preponderance in 
the acid-forming elements, on the contrary, leads to an 
increased urinary acidity and urinary ammonia, 
decreased ability to dissolve uric acid and lowered car- 
bon dioxide tension and alkaline reserve. 
Deficiencies of Vitamines. 
Recent investigations have shown that diets furnish- 
ing sufficient amounts of protein, fat, carbohydrate and 
inorganic salts may yet prove inadequate for growth or 
even for maintenance. Hopkins, (16) feeding rats on puri- 
fied food mixture was unable to obtain any growth until 
he added small quantities of milk or of the ether-soluble 
portion of milk but with this addition growth progressed 
in the normal manner, but it was out of all proportion 
to the energy or protein value of the addition. Five 
substances of this character, called by Funk (17) Vita- 
mines, have been described, two of wliich have definitely 
established a place as essential food factors. According 
to him, pellagra, rickets, scurvy and beriberi are the 
result of a lack of these unidentified but specific 
and indispensable food complexes. 
The first vitamine isolated was the fat soluble A, an 
adequate supply of which is necessary, not only because 
of its stimulating gi'o\vth properties, but because its 
absence produces a serious condition of the eyes and, at 
times, marasmus leading to death. Xerophthalmia is a 
common condition in animals on experimental diets. The 
eyes are swollen, the cornea inflamed and often opaque 
while blindness and death invariably occur unless the die- 
tary error is corrected. McCollum(18) rescued animals 
almost at the point of death by butter or other fat rich in 
this vitamine. Opacities of the cornea are often seen in the 
animals in this and other gardens among ungulates — ^hay- 
(16) Joum. Physiol., 1912, XLIV, 425. 
(17) Die Vitamine und ihre Bedeutung fiir die Physiologie und Pa- 
thologie mit besonderer Beriicksichtigung der Avitaminoses, Wiesbaden, 1914. 
(18) Newer Knowledge of Nutrition, Macmillan, 1919. 
