PROBLEM 1. How to Ckoosc Foods Wisely 187 



your class or club. If you have a school science paper, have your re- 

 sults published. There are a few points that all of these experiments have 

 in common that you ought to know. You must choose animals that are 

 in a good state of health. Wherever possible, the animals should be from 

 the same litter and of the same sex. The animals are then divided into 

 two equal groups. One group receives the diet lacking a particular vitamin 

 while the other group gets the same diet plus the vitamin. You must re- 

 member that the conditions under which you keep the animals are as 

 much a part of the experiment as the diet which you feed them. There- 

 fore, keep them under normal conditions of temperature and in clean 

 cages. Always keep an accurate daily record. Do not cause animals pain 

 or permit them to suffer. These experiments and others can be performed 

 without harm to the experimental animals if you change the diet as soon 

 as evidence of the effect of poor diet is obtained. 



4. What is the effect of the lack of vitamin A upon rats?* Choose 

 rats about three weeks old. Feed one group a diet consisting of the fol- 

 lowing: 



Casein (pure protein) 20% 



Lard (fat) 15% 



Starch (carbohydrate) 56% 



Yeast (for vitamin B) 5% 



Salt mixture (for minerals) 4% 



The salt mixture should be mixed with the other food. Your teacher 

 will help you to get the chemicals you need to make the salt mixture. 



Sodium chloride (NaCl) 5.19 gm 



Magnesium sulphate (MgSO^-yH^O) 16.00 gm 



Sodium dihydrogen phosphate (NaH,PO^-H,0) 10.41 gm 



Potassium hydrogen phosphate (K^HPO^) 28.62 gm 



Calcium lactate 39.00 gm 



Ferric lactate 3.54 gm 



The other group is fed butter instead of lard. When you have achieved 

 your results, return both groups to a normal diet. 



5. What is the effect of the lack of vitamin C upon guinea pigs.^ Feed 

 one group a diet consisting of oatmeal, sterile hay, pasteurized milk, and 

 water. Add orange juice to the diet of the second group. Do the two 

 groups begin to show any signs of difference in activity, in weight, in the 

 condition of the fur? If so, add orange juice to the diet of the first group. 

 How long does it take for recovery? 



* These diets are taken from Adventures in Biology, New York Association of 

 Biology Teachers. 



