146 THE STORY OF GERM LIFE. 



food or drink which we swallow ; those which 

 enter through the nose must be traced to the air; 

 and those which enter through the skin come in 

 most cases through contact with some infected 

 object, such as direct contact with the body of 

 an infected person or his clothing or some objects 

 he has handled, etc. Occasionally, perhaps, the 

 bacteria may get into the skin from the air, but 

 this is certainly uncommon and confined to a few 

 diseases. There are here two facts of the utmost 

 importance for every one to understand : first, 

 that the chance of disease bacteria being carried 

 to us through the air is very slight and confined 

 to a few diseases, such as smallpox, tuberculo- 

 sis, scarlet fever; etc., and, secondly, that the un- 

 injured skin and the uninjured mucous membrane 

 also is almost a sure protection against the in- 

 vasion of the bacteria. If the skin is whole, 

 without bruises or cuts, bacteria can seldom, if 

 ever, find passage through it. These two facts 

 are of the utmost importance, since of all sources 

 of infection we have the least power to guard 

 against infection through the air, and since of all 

 means of entrance we can guard the skin with 

 the greatest difficulty. We can easily render 

 food free from pathogenic bacteria by heating it. 

 The material we drink can similarly be rendered 

 harmless, but we can not by any known means 

 avoid breathing air, nor is there any known 

 method of disinfecting the air, and it is impos- 

 sible for those who have anything to do with 

 sick persons to avoid entirely having contact 

 either with the patient or with infected clothing 

 or utensils. 



From the facts here given it will be seen that 

 the individual's susceptibility to disease produced 



