12 



Insects and Disease 



a great length and migrating through the connect- 

 ive tissue to different parts of the body causing no 

 particular inconvenience until it is ready to lay its 

 eggs when it comes to the surface and then great 

 suffering may result. The African eye-worm is an- 

 other example of a parasite causing mechanical 

 injury only at certain times. It works in the 

 tissues of the body sometimes for a long while, 

 doing no harm unless it finds its way to the connect- 

 ive tissue of the eyeball. 



It is known that many of the germs which cause 

 diseases cannot get into the body unless the pro- 

 tecting membranes have first been injured in some 

 way. Thus the germs that cause plague and lock- 

 jaw find their way into the system principally 

 through abrasions of the skin. Many physicians 

 have come to believe that the typhoid fever germ 

 cannot get into the body from the intestine where it 

 is taken with our food or drink unless the walls of 

 the intestine have been injured in some way. It is 

 well known that of the many parasites that inhabit 

 the alimentary canal some rasp the surface and 

 others bore through into the body cavity. This in 

 itself may not be a serious thing, but if the mechani- 

 cal injury thus caused opens the way for malignant 

 germs, baneful results may follow. Even that 

 popular disease appendicitis is believed to be due 



