of something — a something removed during the poHshing. What that some- 

 thing is Eijkman did not know. But he showed that to keep an animal in 

 health something is necessary besides proteins and fats and carbohydrates. 



For ten or fifteen years following, Dr. Frederick Gowland Hopkins 

 (1861- ) of Cambridge University was feeding rats on a diet of the 

 several substances that make up cow's milk. He used pure casein, pure 

 butterfat, pure lactose (milk sugar), and the purified minerals present in 

 milk. He tried to account for everything. While the rats fed on cow's milk 

 thrived, those fed on the combination of purified nutrients appeared mis- 

 erable and deficient. Hopkins added a few drops of "real milk" each day 

 to their synthetic diet and made these sickly rats well again. A "balanced 

 diet" containing the usual organic nutrients and the necessary minerals is 

 obviously not sufficient. Something must be present in the cow's milk that 

 is not present in die artificial combination of fats, proteins, and minerals. 

 What was this "accessory factor", as Hopkins called it ? 



Later, a Polish scientist, Casimir Funk (1884- ), having made similar 

 observations in the laboratory, suggested for this "unknown something" the 

 name vitamine — vital because it is essential to life; and amine because he 

 assumed it to be one of a class of compounds characteristic of the structure 

 of proteins, namely, amines or amino acids (see page 99). This name 

 (spelled now without the e) has continued in use, although the substances 

 are not amines at all, and although it applies to a growing series of substances. 



The experimental work has continued, and has become greatly ex- 

 panded. The typical procedure is illustrated by the study of scurvy in 

 guinea-pigs^ (see illustration opposite). Later research attempted to answer 

 the questions How much of a given vitamin is necessary for a pound of 

 live animal } and What is a vitamin, anyhow ? 



What Do Vitamins Do? 



Indirect Action We know that vitamins are organic compounds 

 which are essential in the diet of at least the higher animals. Unlike pro- 

 teins and mineral salts, they cannot be considered as building materials. 

 Unlike the other organic foods — fats, carbohydrates and proteins — they can- 

 not be considered sources of energy. Yet without vitamins normal metab- 

 olism cannot take place. 



Without increasing protoplasm or supplying energy, vitamins do influ- 

 ence metabolic processes. In this respect they are like the hormones pro- 

 duced within the body (see pages 302-304). Like the hormones, the 

 vitamins produce effects highly disproportionate to the amount present. 



^The guinea-pig is not a pig at all, but a rodent — more like a rabbit. Nor is it from 

 Guinea, being a native of South America. Its proper name is cavy. 



107 



