The Protection of Health 591 



automatically the hands touch the face and lips and eyes, and 

 how easily minute germ-infected particles of dust and moisture 

 may be transferred from hands to face. A healthy person 

 may touch some infected article or person and carry the infec- 

 tive germs eventually to the face, eyes, or lips, or to some 

 abrasion in the skin. Or they may transfer the germs to some 

 common utility, as a towel or dish, and thus make possible their 

 transfer to another person. Food, such as milk, fruit, bread, 

 cakes, and candies, may be infected by handling with un- 

 washed hands. 



291. Resistance to disease. The constitution of the in- 

 dividual who receives the infective organisms is very important 

 in respect to the growth of the germs and the development of 

 the disease. An individual may be immune, that is, resist 

 successfully the invading germs and the disease. Immunity 

 varies in degree from partial to total. It may be due generally 

 to the following causes. 



I. It may be natural, that is, due to a constitution inherited 

 from stalwart, disease-resisting family and race. This is aided 

 by maintaining a general condition of health and vigor through 

 proper diet and hygiene. 



II. (1) It may be acquired in recovery from a former attack 

 of certain diseases, such as chicken pox, smallpox, measles, 

 scarlet fever, typhus fever, mumps, plague, cholera, and typhoid 

 fever. 



(2) It may be acquired artificially by specific treatment, as 

 by vaccination, or inoculation of specific serum containing 

 bacteria or bacterial products, or both. 



Immunity when acquired either in the recovery from a given 

 disease or artificially through vaccination is always specific. 

 One who has recovered from an attack of the mumps is specifi- 

 cally immune against mumps, but not against any other dis- 

 ease. Vaccination against smallpox or typhoid fever develops 

 specific immunity against smallpox or typhoid fever. 



Degrees of resistance. An individual may on the contrary 



