Biochemical and Biophysical Phenomena 771 



diet, the mice died. However, when milk was added to the prepared 

 diet, the animals lived. Lunin concluded that milk contained an un- 

 known substance which must be present in a diet to maintain life. 



In 1913, McCollum and Davis and Osborne and Mendel independ- 

 ently announced results of experiments showing that there is a sub- 

 stance in butterfat which promotes the growth and well-being of rats. 

 Thus was discovered a fat-soluble dietary substance which is essential 

 for satisfactory animal nutrition. The substance was first known as 



Fig. 372. — Pellagra, which means "skin seizure," is a dietary disease of man 

 caused by the deficiency of nicotinic acid (niacin) (of the vitamin B complex). 

 Skin lesions are characteristic of pellagra, in addition to diarrhea, anemia, and 

 lesions in the central nervous system producing mental confusion, dementia, and 

 mania. (From Stitt: Diagnostics and Treatment of Tropical Diseases. Courtesy 

 of P. Blakiston's Son & Co.) 



