PARASITIC BACTERIA. 147 



by parasitic bacteria will depend upon his habits 

 of cleanliness, his care in handling infectious 

 material, or care in cleansing the hands after such 

 handling, upon his habit of eating food cooked 

 or raw, and upon the condition of his skin and 

 mucous membranes, since any kind of bruises 

 will increase susceptibility. Slight ailments, 

 such as colds, which inflame the mucous mem- 

 brane, will decrease its resisting power and ren- 

 der the individual more susceptible to the entrance 

 of any pathogenic germs should they happen to 

 be present. Sores in the mouth or decayed teeth 

 may in the same way be prominent factors in the 

 individual's susceptibility. Thus quite a number 

 of purely physical factors may contribute to an 

 individual's susceptibility. 



Resisting Power of the Body. Even after the 

 bacteria get into the body it is by no means cer- 

 tain that they will give rise to disease, for they 

 have now a battle to fight before they can be sure 

 of holding their own. It is now, indeed, that the 

 actual conflict between the powers of the body 

 and these microscopic invaders begins. After 

 they have found entrance into the body the bac- 

 teria have arrayed against them strong resisting 

 forces of the human organism, endeavouring to 

 destroy and expel them. Many of them are rapid- 

 ly killed, and sometimes they are all destroyed 

 without being able to gain a foothold. In such 

 cases, of course, no trouble results. In other 

 cases the body fails to overcome the powers of 

 the invaders and they eventually multiply rapidly. 

 In this struggle the success of the invaders is not 

 necessarily a matter of numbers. They are sim- 

 ply struggling to gain a position in the body, where 

 they can feed and grow. A few individuals may 



