UNICELLULAR FORMS 87 



bacteria most of them also kill the human cells. If a chemical could 

 be found that would destroy pathogenic bacteria and not adversely 

 affect the human cells, then the treatment of disease would be con- 

 siderably simplified. In recent years certain successes have been 

 attained. Some drugs now obtainable are very effective in destroy- 

 ing bacteria in concentrations that apparently are without injurious 

 effect on the human body. Treatment with chemicals in attempting 

 to destroy invading micro-organisms is known as chemotherapy. 



Many pathogenic bacteria are killed by heat without great diffi- 

 culty. Thus if milk is heated to 50° C, the typhoid bacteria and 

 allied forms are killed. This process of partially sterilizing milk by 

 low temperature heating was developed by the great French bac- 

 teriologist, Pasteur; hence the name, pasteurize. However, some 

 types of bacteria when in a dry or otherwise unfavorable environ- 

 ment form spores that are highly heat resistant and withstand dry- 

 ing for a long time. Some spores are able to withstand heat above 

 the boiling point of water for an hour or more. But if the tempera- 

 ture is reduced to a point compatible with their normal life, the 

 spores develop into active bacteria. So, in intermittent steriliza- 

 tion, the food or other material is heated to the death point of 

 active bacteria, then allowed to cool, then re-heated after allowing 

 sufficient time for the spores to develop into active forms, the 

 process being repeated several times. Thus all the inactive and 

 resistant spores are induced to become active bacteria and are then 

 killed. 



Some bacteria in their energy-transforming metabolism are un- 

 able to use the oxygen of the air, but derive their energy by an 

 energy-releasing reaction system that is too complicated to discuss 

 here. These are obligatory anaerobes. The tetanus bacillus is of this 

 type. Not only are such organisms unable to utilize the oxygen of 

 the air, but, curiously enough, atmospheric oxygen acts on them as 

 a poison. So in deep wounds, when the air is shut off, tetanus 

 bacilli find conditions suitable for growth. It is for this reason that 



