138 MAN, — THE ANIMAL 



The bacteria or germs which cause many of the 

 common diseases in man and animals are abundant 

 in nature and commonly found where man lives. 

 An examination of any group of men will usually 

 show the presence of many of the commoner bac- 

 teria in the body although none of the men thus 

 examined may be suffering from any disease. 

 This leads to the second inquiry, How does man 

 recover from a disease and why is he not sick all 

 of the time if he harbors disease producing bac- 

 teria? 



Recovery and the resistance to disease exhibited 

 by living things introduce us to one of the most 

 distinctive phases of living protoplasm. Disease 

 has been known from remote times and yet nu- 

 merous plants, animals and men inhabit the globe. 

 These have survived the ravages of disease or 

 have never succumbed to their poisons. It it well 

 known that there is a natural resistance to disease 

 which is held unequally by man and animals and 

 plants; some men are never sick and others seem 

 to be unable to resist any form of disease. Again 

 the powers of resistance are higher under certain 

 conditions than others. This power to resist the 

 organisms that invade the body is called immunity. 

 It is one of the fundamental characteristics of all 

 living things. Immunity has two general aspects: 

 resistance to the microorganisms themselves and 

 resistance to the microbial poisons or toxines. 



