170 THE VITAMINS 



per cent of the ration. This diet supports excellent growth up to the 

 time of the onset of scurvy. 



Sound mature oats show no antiscorbutic property when fed to 

 guinea pigs and are eaten readily by them. By using heated skimmed 

 milk and fresh butterfat instead of heated whole milk, the absence of 

 antiscorbutic vitamin is at least equally well ensured and the palatability 

 of the diet and its fat-soluble vitamin content are improved. The heat 

 treatment necessary to ensure complete destruction of vitamin C in 

 the skimmed milk powder should be determined by each investigator 

 for his own material and technique, keeping in mind the likelihood of 

 variation in antiscorbutic vitamin content of milk with the season 

 and the importance of eliminating this vitamin completely from the 

 basal ration without subjecting the food to such excessive heating as 

 would give it a burnt taste and prevent its being eaten readily by the 

 experimental animals. In these experiments, two hours' heating at 

 110° C. in shallow trays freely exposed to the air of the oven was 

 found to be sufficient, as determined by controlled feeding experi- 

 ments. After such heating the milk powder is of a light brown color. 



The butterfat, prepared by melting butter of good quality at the 

 lowest possible temperature and freeing from water and curd by de- 

 cantation and filtration through paper, is intimately mixed with the 

 heated milk powder, the salt, and the freshly ground oats, so that the 

 constituents of the mixture cannot be separated by the experimental 

 animal while eating. The food mixture should be kept in a refrigerator 

 in well-filled, air-tight containers; fresh portions fed daily, and feed- 

 ing cups thoroughly cleansed at least twice a week. Even the slightest 

 incipient rancidity may result in failure of the animals to eat the food 

 readily, in which case the interpretation of results will be difificult and 

 probably of very doubtful value. 



Selection and Care of Experimental Animals. — The experimental 

 animals should either be bred by the investigator or purchased at an 

 early and known age. They should be known to be growing at a normal 

 rate. For about a week before the beginning of the experimental period 

 they should be housed in the experimental cages or pens and fed with 

 the above basal ration plus green food, both ad libitum. The experi- 

 ment proper is then begun by simply discontinuing the green food with or 

 without the feeding of a measured amount of antiscorbutic in addition 

 to the basal ration. Guinea pigs six to eight weeks old and weighing 

 300 to 350 grams are best used for this purpose. Placed at this age 

 and size upon the above basal diet with food and water always avail- 

 able they usually eat about 18 to 20 grams of the dry food mixture per 



