THE GROWTH OF BACTERIA 457 



We also hear a good deal nowadays about the increase in the 

 length of the life span. In every country except India in which 

 vital statistics are available the expectation of life is steadily 

 lengthening. In England, for example, in the decade between 1870- 

 1880 the average expectancy of life for a child at birth was 42.98 

 years. In 1922 it was 56.95 years. In Massachusetts, where 

 vital statistics have been kept for a longer period than some other 

 states, in 1855 the expectancy of life was 39.77 years, in 1920 it 

 was 55.25. In the United States (registration area), in 1901, the 

 expectancy of life was 49.24 years, in 1926 it was 57.74 years, 

 and at the present time it is over 58 years. Why is this so? 

 Principally because we are gaining mastery over the diseases 

 caused by bacteria and especially diseases of young children. 

 Dr. Vincent of the Rockefeller Foundation said recently that 80 

 per cent of the illnesses of man could be avoided if people were 

 willing to obey health laws and live as well as they know how. 

 Then, too, we are learning that health is closely associated with 

 conditions in man's environment and that it pays from every view- 

 point to have good sanitation and housing. We are learning to 

 quarantine the sick, so that diseases may not be so easily com- 

 municated as in the past. And we have built many and vast 

 " temples of healing " — hospitals and sanitariums, where the sick 

 are brought back to health. 



PROBLEM I. HOW MAY WE CONTROL THE GROWTH OF 



BACTERIA? 



Demonstration 1. To show the effect of temperature on the growth 

 of bacteria. 



Number four tubes containing bouillon. Place number one in 

 the ice box, number two in a dark box at a moderate temperature, 

 number three in a box at a hot temperature (120° F. or over), and 

 boil number four for 15 minutes and then place with number two. 



Note in which tube the greatest amount of growth takes place. 

 Note the odor as well as the color of bouillon. Note in which tube the 

 least growth takes place. 



Describe the effect of intense heat on bacteria? Would the sand 

 of a desert contain many bacteria? The ice of the polar regions? 

 From this experiment we derive the very important method of fighting 

 bacteria by means of sterilization. Give a definition of sterilization. 



