460 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 



is another preservative. It, like salt, changes the flavor of mate- 

 rials kept in it and so cannot come into wide use. Spices are also 

 all used as preservatives. 



Harmful preservatives. Certain chemicals and drugs, used as 

 preservatives, seem to be on the border line of harmfulness. Such 

 are benzoic acid, borax, and boracic acid. These chemicals may 

 be harmless in small quantities, but unfortunately in canned 

 goods we do not always know the amount used ; also, as a rule, 

 food that needs such a preservative is of bad quality in the first 

 place. The Pure Food Law makes it illegal to use any of these 

 preservatives in food (excepting very small amounts of benzoic 

 acid). Food which contains this preservative must be so labeled 

 and should not be given to children or people with weak digestion. 

 Unfortunately, people do not always read the labels, and thus the 

 Pure Food Law is ineffective in its working. 



Demonstration 3. To determine the most effective disinfectants. 



Inoculate test tubes containing bouillon with germs from a Petri dish 

 culture. Number and label the tubes. Expose all tubes, unplugged, 

 to air. 



To tube one add 1 drop formalin, 

 two add 5 drops formalin, 

 three add 1 drop lysol. 

 four add 3 drops lysol. 

 five add 1 drop iodine, 

 six add 5 drops iodine, 

 seven add 4 drops carbolic acid, 

 eight add 10 drops carbolic acid, 

 nine add 1 drop bichloride mercury solution, 

 ten add 5 drops bichloride mercury solution, 

 eleven add 5 drops mercurochrome. 

 twelve add 15 drops mercurochrome. 



Tabulate daily, for a week or more, the results for the contents of each 

 tube on a table. 



Which of the above is the best disinfectant? Why do you answer 

 as you do? (Remember that according to definition an antiseptic may 

 retard the growth of bacteria but will not of necessity kill them; a 

 germicide destroys all bacteria if used properly; while a disinfectant 

 is a solution used to kill disease germs, usually in the excreta of sick 

 people.) 



Practical Exercise 2. Using the data from the preceding demonstration, 

 classify the materials used, as antiseptics, germicides, or disinfectants. Give 

 a reason for each. 



