86 
HOUSEHOLD BACTERIOLOGY 
Sources of 
Infection 
it is put into a refrigerator or in any way used for the 
storage of food. Safety may be assured if ice is never 
allowed to touch the food. Its effects can be obtained 
without actual contact and contact may mean con¬ 
tamination. 
The tub of lemonade standing open on the picnic 
ground or the street corner has sufficient chance of 
germ infection without a block of doubtful ice in its 
midst. 
THE RESISTANCE OF THE BODY TO DISEASE GERMS 
We have seen that many diseases which afflict hu¬ 
man beings have been definitely traced to these or¬ 
ganic forms; to these micro-organisms found in in¬ 
haled dust, in polluted water, in food and on articles 
which may puncture the skin. 
If the avenues of infection are so common, the ques¬ 
tion naturally arises, how can any human being escape ? 
We know that many do, that there are hundreds of 
persons who never have had typhoid fever, diphtheria, 
or other infectious disease; that two persons may, so 
far as we know, eat of the same food, drink from the 
same water supply or live under exactly similar con¬ 
ditions—one has some infectious disease, the other re¬ 
mains well. 
It is too a matter of common knowledge that a de^ 
gree of safety from a second attack is often assured to 
the person after recovery from the first illness. He 
seems to have some power of resistance which he did 
not have before and which is absent in his neighbor. 
