IMPORTANCE OF BALANCED DIET 



85 



_ Water 



FIG. 125. WHAT A BOT- 

 TLE OF MILK CONTAINS 



also deficient in several vitamins, especially vitamin 

 D. Calcium and phosphorus cannot be utilized prop- 

 erly for the building of bones and teeth unless vitamin 

 1) is present. This is one of the reasons some children 

 have bowlegs, deformed chests, or curvature of the 

 spine. In 1927 two noted scien- 

 tists, Dr. Harry Steenbock and 

 Dr. Alfred Hess, discovered a 

 method of increasing the vita- 

 min D content of foods by means 

 of ultra violet rays. As a result 

 of this famous discovery it is 

 now possible in many communi- 

 ties to buy milk which has been 

 enriched with "sunshine" vita- 

 min D. 



Every person should include 

 milk in his diet. Growing chil- 

 dren should consume at least one 

 quart of milk daily. 



How can we provide ourselves with pure milk? It 

 is common knowledge that milk sours and curdles 

 readily unless it is kept very cold. Do you know the 

 reason for this? Bacteria thrive well in warm milk. 

 Bacteria that get into milk feed upon the sugar, lac- 

 tose, and change it into lactic acid. All acids have a 

 sour taste, and this is the reason spoiled milk tastes 

 sour. As the acid increases, it causes the proteins to 

 form lumps or curds, or as we commonly say, the 

 milk curdles. You can demonstrate this fact at home 

 or in the laboratory. Put some fresh milk into a 

 tumbler or a test tube. Add a few drops of dilute 

 hydrochloric acid and observe what happens. 



The bacteria that cause milk to sour are not harm- 

 ful to man, but unfortunately bacteria which produce 

 certain diseases may be present in milk. If a cow has 

 tuberculosis, the bacteria which cause the tubercu- 

 losis may get into the milk. A test has been perfected 

 which will reveal the disease if the cow has contracted 

 it. Many states now have regulations which require 

 dairy herds to be tested for tuberculosis at regular 

 intervals. Such cows as show by test that they are 

 afflicted with the disease should be removed from the 

 herd at once. 



Epidemics of typhoid fever, diphtheria, and several 

 other diseases have sometimes been traced to the 

 community milk supply. Cows do not have these dis- 

 eases ; therefore, the milk as it is taken from the cow 

 is free of these disease-producing bacteria. The dis- 

 ease bacteria get into the milk through careless 

 handling, frequently from the hands of people who 

 have the disease or from unclean containers in which 

 the milk is placed. 



Great care should be taken around the farm to 

 insure clean milk. Stables should be painted or white- 



washed. Manure should never be allowed to remain 

 in the barn. All windows should be screened. All con- 

 tainers used to hold milk should be scalded with boil- 

 ing water. Persons who milk cows should wear clean 

 white clothing and should wash their hands before 

 each milking. The udders of cows should be wiped 

 with a mild disinfectant. 



Milk is obtainable in different forms and under dif- 

 ferent conditions. If it is used directly from the dairy 

 without having been treated in any way it is called 

 raw milk. If raw milk is obtained and handled under 

 guaranteed sanitary conditions it is usually sold un- 

 der the name of certified milk. 



International News Photos, Inc. 



FIG. 126. SANITARY DAIRY 



Since milk is so easily infected with bacteria much 

 of it today is pasteurized before it is distributed to 

 the consumer. The process consists in heating the 

 milk to a temperature of from 142 F. to 150 F. and 

 keeping it at this temperature about thirty minutes 

 and then cooling rapidly. This treatment kills bac- 

 teria and safeguards the public from disease germs 

 carried by milk. 



REFERENCES FOR FURTHER STUDY 



Texts 



Caklwell and Curtis, Science for Today, Chap. 35 

 Clement, Collister, and Thurston, Our Surroundings, Chaps. 



26-33 

 Hunter and Whitman, My Own Science Problems, Unit 1 1 ; 



Science in Our World of Progress, Unit 15 

 Lake, Harley, and Welton, Exploring the World of Science, 



Chaps. 26, 27 

 Pieper and Beauchamp, Everyday Problems in Science, Unit 



4 

 Powers, Neuner, and Bruner, The World around Us, Chap. 



22; This Changing World, Unit 6; Man's Control of His 



Environment, Chap. 28 



