394 PRACTICAL HYGIENE 



lives, or one's method of gaining a livelihood, that produce 

 changes in the body, imperceptible at the time, but, in the 

 long run, laying the foundations of disease. And last, 

 and most potent, are the minute living organisms, called 

 microbes or germs, that find their way into the body. 

 Although there are two general kinds of germs, known as 

 bacteria (one-celled plants) and protozoa (one-celled ani- 

 mals), most of our germ diseases are caused by bacteria. 



Effects of Germs. While there are many kinds of germs 

 that have no ill effect upon the body and others that are 

 thought to aid it in its work, there are many well-known 

 varieties that produce effects decidedly harmful. They 

 gain an entrance through the lungs, food canal, or skin, 

 and, living upon the fluids and tissues, multiply with great 

 rapidity until they permeate the entire body. Not only do 

 they destroy the protoplasm, but they form waste products, 

 called toxins, which act as poisons. Diseases caused by 

 germs are known as infectious, or contagious, diseases. 1 

 The list is a long one and includes smallpox, measles, 

 diphtheria, scarlet fever, typhoid fever, tuberculosis, la 

 grippe, malaria, yellow fever, and others of common oc- 

 currence. In addition to the diseases that are well pro- 

 nounced, it is probable that germs are responsible also for 

 certain bodily ailments of a milder character. 2 



1 " An infectious disease is one in which disease germs infect (that is, invade) 

 the body from without. Among the infectious diseases are some that are quite 

 directly and quickly conveyed from person to person and to these the term conta- 

 gious is applied. Formerly a sharp line was drawn between infection and conta- 

 gion, but to-day it is recognized that no such line exists." HOUGH AND SEDG- 

 WICK, The Elements of Hygiene and Sanitation. 



2 The arctic explorer, Nansen, states that during all the time that his party was 

 exposed to the low temperature of the arctic region, no one was attacked by a cold, 

 but on returning to a warmer climate they were subject to colds as usual. The 

 difference he attributes to the absence of germs in the severe arctic climate. 

 There seems to be no doubt but that most of our common colds are due to attacks 

 of germs. 



