4 Microbes and You 



depend upon other living things for their food and for their very 

 existence. Man's diet has been broadened as the result of micro- 

 bial activity in the manufacture of such things as cheeses, sauer- 

 kraut, pickles, beer, and leavened bread, to mention but a few. 



Once it had been established that bacteria were not "animal- 

 cules," as Antony van Leeuwenhoek (1632-1723) designated them 

 in the seventeenth century, this new branch of plant science 

 appropriately found its way into the field of botany, where it still 

 remains as an ugly-duckling in some institutions. Botanists do not 

 employ the same technics as those used by microbiologists, so it 

 was only natural that the new science should eventually break 

 away from botany and stand on its own tsvo feet. 



It seems unfortunate that so many bacteria in the distant past 

 became unhappy with their saprophvtic existence and decided to 

 become pathogens, invading the tissues of plants and of animals. 

 But this characteristic of microorganisms has presented one of the 

 great challenges to microbiologists in the search for new ways to 

 lengthen the span of man's life to the Biblical three score years and 

 ten. We have come astonishingly close to this goal in recent years 

 as the following statements will indicate. 



Actuarial figures released by a large life insurance company 

 demonstrate in a clear fashion the influence of scientific progress on 

 the life span. The expectation of life at birth is five years greater 

 today than it was a decade ago, and double that existing between 

 1879-1889, the earliest period for which experience tables are 

 available. In round numbers, since 1911 we have gained some- 

 thing over twenty-one years, and since 1879 the average human 

 life has been prolonged by thirty-five years! This is primarily a 

 victory for preventive medicine, with a heavv assist in recent years 

 from antibiotics. It is also a victory for nutritionists, who in the 

 past two decades have told us more about what is good for us to 

 eat than we ever knew before. An average human life two 

 thousand years ago was about twenty-five years. In 1900 this 

 figure had climbed to forty-nine and today we can look forward to 

 better than sixty-eight years of life, females, on the average, living 

 longer than males. 



