256 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



Take special care to conserve the vitamin Bi in foods during cooking. Many 

 of the foods that contain an abundance of vitamin Bi are cooked before being 

 eaten, and next to vitamin C, vitamin Bi is the vitamin most likely to be lost 

 when foods are cooked or canned. The precautions necessary to conserve vita- 

 min Bi will conserve other vitamins as well. 



4. Store foods at low temperatures and in closed containers. 



5. Do not chop or crush fresh fruits and vegetables and allow them to stand. 

 They lose vitamin C rapidly. 



6. Frozen foods have practically the same vitamin content as fresh ones. 

 Care must be taken to conserve it during preparation for serving. Do not 

 defrost and then allow to stand. If frozen foods are to be cooked put them on 

 to cook while they are still frozen and use all of the liquid. 



7. Dried foods are not especially recommended for vitamin value. 



8. Canned foods retain vitamin value well, with the possible exception of 

 vitamin C, provided they have not been stored too long. To obtain full value, 

 use the entire contents of the can. Canned foods are cooked foods and should 

 be treated accordingly. 



9. In canning foods observe the same precautions for conserving vitamin 

 content as suggested for cooking. 



VITAMIN VALUES 



As soon as the existence of any one of the vitamins was recognized 

 it became a matter of concern to know not only in what foods it oc- 

 curred but also in what quantities. The development of methods of 

 measurement was, therefore, of considerable importance. Chemical 

 identification of the vitamins has usually not been made until some 

 time after their discovery and for this reason development of chemi- 

 cal or physical methods of measurement proceeded uncertainly. 



Many of the studies on the physiological effects of the vitamins 

 have been made with laboratory animals. It was natural in some of 

 these studies for information to be obtained on the relation between 

 the quantity which an animal ate of a food known to contain a par- 

 ticular vitamin and the response of that animal in terms of growth, 

 or cure or prevention of the disease associated with the vitamin. As 

 these observations were made, consideration was given to the possi- 

 bility of using a relationship of this kind as the basis of a quantita- 

 tive method of measurement for the vitamin concerned. Methods of 

 determination in which the reactions of animals are used are called 

 biological methods. 



To determine actual vitamin content by a biological method it is 

 necessary to carry out a test in comparison with a substance con- 

 taining a known amount of the vitamin in question. Wlien the bio- 

 logical methods were first suggested, this condition could not be 

 met because the chemically pure vitamins had not yet been prepared 

 and natural products vary too much to be used as reference mate- 

 rials. As a result of this situation it became the custom to express 

 content with respect to a particular vitamin in terms of the quantity 



