THE BACTERIA 203 



and, upon the return of favorable conditions, may grow and 

 produce the kind of cell which formed it. Such specially pro- 

 duced reproductive cells are called spores. They often enable 

 the bacteria and other plants to live through periods of un- 

 favorable conditions as drought, lack of proper air, absence 

 of suitable food, and unfavorable temperature. Some kinds 

 can withstand freezing or boiling temperatures. It is much 

 more difficult to destroy the spores of bacteria than the vege- 

 tative, or growing, cells. There are very few spore-forming 

 bacteria among those that produce diseases of men. This is 

 fortunate, since the problem of combating disease would be 

 much more complex if all the harmful bacteria should be able 

 to form these resistant spores. A,, disease known as anthrax 

 oft'ers a good illustration of the way in which spore formation 

 may increase the distribution of disease. Anthrax is a very de- 

 structive disease, as is shown by the fact that, prior to the use 

 of the treatment devised by Louis Pasteur, France in single 

 years has lost as much as $20,000,000 worth of cattle and 

 sheep. The disease also affects men and may cause their 

 death, as it does that of cattle, sheep, and other animals, in 

 from a few hours to a few days after infection. The spores of 

 anthrax form only when the bacteria are exposed to the air. 

 When an animal dies of anthrax, if its body decays while ex- 

 posed to the air, millions of anthrax spores are formed. These 

 spores can lie in the field for very long periods, probably 

 several seasons, and withstand the variations in temperature, 

 moisture, and light When they are introduced into the ali- 

 mentary tract of an animal, they soon reach the circulatory 

 system, where they grow with surprising rapidity and may 

 soon cause the death of the newly infected animal. The de- 

 sirability of the complete destruction of bodies of animals that 

 have died of anthrax is evident. 



190. Bacterial decay and its significance. The bacteria and 

 certain other dependent organisms (as molds, yeasts, and 

 many animals), while living upon the bodies or the products of 

 plants and animals, use parts of them as food. The processes 



