There are two scales used in thermometry, the Fahrenheit and the Centigrade. The former is generally used. However, since many of the scientific calculations are made using the Centigrade scale it is wise for the nurse to understand how to translate one to the other. Centigrade has 0 deg. as the freezing point and 100 deg. as the boiling point, while Fahrenheit has 32 deg. as freezing point and 212 deg. as boiling point. To change Fahrenheit to Centigrade it is necessary to subtract 32 from 212 in order to make the freezing points correspond. This would read 212-32 = 180 deg. F. = 100 deg. C; hence a degree Centigrade represents 5/9 of a degree Fahrenheit. To change Centigrade to Fahrenheit it is necessary to remember that every Fahrenheit degree is 9/5 times as large as the Centigrade and the addition of 32 deg. must also be made. For example: Change 105 deg. F. to Centigrade: 105 deg.-32 deg. x 5/9 = 41 deg. C. Change 50 deg. C. to Fahrenheit: 50 deg. x 9/5 + 32 deg. = 90 deg. + 32 deg. = 122 deg. F. FOOTNOTE: [28] "Diseases of Nutrition and Infant Feeding," by Morse and Talbot. CHAPTER V FOOD MATERIALS AND THEIR PREPARATION ~Dairy Products.~--Milk, cream, and other dairy products form such an important part of the invalid dietary that they require especial care in their selection. "Certified Milk" is the safest. This is protected by special inspection. The methods and standards governing the production and distribution of certified milk were adopted by the American Association of Medical Milk Commissions, May 1, 1912. The sanitary condition of the dairy, the cleanliness of the vessels into which the milk is placed, the health of the milkers, and a surety that no member of their family with whom they come in contact has any kind of contagious disease, are all obligatory. The feed for the cows and the purity of the water given them to drink must be inspected and made to conform to the standard laid down for certified milk. The milk of sick cows and those having tuberculosis is absolutely condemned. The composition of certified milk is standardized as follows: the fat standard shall be 4%, with a permissible range varying from 3.5% to 4.5%. The proteins shall be 3.5%, with a permissible range varying from 3% to 4%. Certified milk shall not contain more than 10,000 bacteria to the cubic centimeter when it is delivered. This inspection and standardizing necessarily raises the price of certified milk above that of milk not so rigidly cared for, and when the additional expense makes it impossible for the patient to afford certified milk, the only thing to do is to be sure of the reliability of the dealer from whom the milk is purchased and the cleanliness of the dairy from which it is procured. Buttermilk and butter are the milk products which require some attention as to selection. The former grows sour with age and the odor of advanced fermentation and decomposition is readily recognized.