MEANS OF BACTERIAL INVASION 235 



are small ; that our fathers and grandfathers have con- 

 sumed similar foods for generations and have suffered 

 only occasionally therefrom. It is therefore wiser not to 

 be over alarmed or to make life burdensome by too great 

 precautions, but simply to use such care as may seem 

 feasible and possible in our homes, and not give up the 

 use of any desirable food because we know that it may 

 be an occasional source of danger. Some people have 

 actually given up the use of butter and milk because it 

 has been shown that they contain so many bacteria. Such 

 a procedure is sheer nonsense. The facts here outlined 

 have been given, not for the purpose of inducing people 

 to avoid the use of such materials, but merely to suggest 

 to them the wisdom of adopting possible precautions 

 against consuming contaminated foods. 



3. Means of Invasion 



A matter of almost equal importance in considering the 

 distribution of disease is the means by which the bacteria 

 get into the body. Each species may have its own means 

 of entering, and frequently each can find entrance in only 

 one way. If it should get in by other means it would pro- 

 duce no injury. Some species, however (tuberculosis), pro- 

 duce trouble, no matter how or where they enter. If we 

 know the means of entrance of any contagious material, 

 we are of course in a much better position to guard our- 

 selves against it. The important means of entrance are 

 as follows. 



The Skin. Some diseases find entrance chiefly through 

 the skin. This is true of the bacteria which cause the 



