72 ADVANCED PHYSIOLOGY 



trouble there, though the same sort cannot injure man. 

 Further, it is well known that some people " catch" diseases 

 more easily than others. Some people, indeed, although 

 again and again exposed to diseases, do not take them, 

 while others under the same conditions take them easily 

 enough. . 



Lastly, in the case of some diseases, such as scarlet fever, 

 mumps and whooping cough, if a person has them once and 

 recovers, he is not likely to have them again even though 

 exposed to them. Such persons are immune against a second 

 attack of these diseases. Immunity is a condition which 

 enables a person to resist diseases when exposed to them. The 

 greater one's power to withstand diseases, the more secure 

 is his health. 



There are various methods by which immunity can be 

 produced; one factor only need be mentioned here. 



Resisting power varies with the physical condition of the per- 

 son. One in good health, with strong vitality, is less liable to 

 take the germ diseases than one who is less robust and vigorous. 

 Out-of-door life, and the eating of wholesome foods are, thus, 

 among our greatest safeguards against them. Especially 

 has it been shown that alcohol tends to lower this power of 

 resistance, and persons addicted to the use of alcoholic bever- 

 ages are more liable to yield to the attack of infectious dis- 

 eases than are those who refrain from their use. The reasons 

 for this are not wholly known. It is certain that alcohol 

 is primarily a poison, acting directly upon the living cells 

 so as to interfere with their normal functions. Resistance to 

 disease is dependent upon the activities of the cells, and it 

 is natural to conclude that if alcohol acts in any degree as a 

 cell poison it will interfere with this resisting power. At all 

 events, the facts are certain; and the more frequent the use 

 of alcohol, the less is one's power of resistance to harmful 

 bacteria. 



