xix BACTERIA AND DISEASES 285 



194. Disease Germs in the Body. It is impossible to 

 keep out of the way of the many disease germs that 

 surround us at all times. We breathe, eat, drink, and 

 touch these little organisms every day and so cannot 

 avoid taking them into our bodies. Why, then, are we not 

 sick oftener? It is because the human body has a 

 wonderful power of defense against germs of all kinds 

 as long as it is kept in a good physical condition. It 

 does not let the germs grow and produce disease if it 

 can possibly help it. 



If the body has the power to resist the action of 

 bacteria, we say it is immune to tJie disease. Natural 

 immunity is due to a high degree of vitality in all tissues 

 and cells of the body and is thought to be inherited. 

 Among the agencies and conditions that make the body 

 subject to the invasion of disease germs we may men- 

 tion poor or insufficient foods and impaired digestion ; 

 fatigue and exhaustion ; exposure to cold, filth, and 

 unhygienic surroundings; vicious habits and drunken- 

 ness ; and, in fact, everything that tends to disturb the 

 functions of any organ of the body. On the other 

 hand, an abundance of good, wholesome food and pure 

 water, an adequate supply of pure, fresh air, a sufficient 

 amount of physical and mental exercise and rest, clean- 

 liness, so*briety, and moderation, and, in short, a life well 

 regulated in all respects, tend to fortify the body against 

 such diseases. 



We do not know just how the body destroys the germs 

 or how it resists the action of the poisons which they 

 produce, but we do know that the white corpuscles of 



