No. 4.] AGRICULTURE AND PIEALTH. 275 



Moses applied it many centuries ago in the preventive 

 treatment of leprosy and in the management of camp life. 

 In the middle ages nineteen thousand lazarettos were neces- 

 sary to provide shelter in continental Europe for the out- 

 casts from this disease. Dr. Jenner applied it when he 

 introduced the practice of vaccination for the prevention of 

 small-pox, a hundred years ago. But it is only within the 

 past half-century that systematic and careful study and at- 

 tention have been given to public hygiene, with the view of 

 training young men in the science of preventive medicine, 

 or the art of prolonging life. It is a fact capable of easy 

 demonstration, that, since careful attention has been given 

 to the subject of preventing the spread of infectious diseases 

 by means of notification, isolation, disinfection and vaccina- 

 tion, and still more recent methods of treatment and pre- 

 vention by means of the taking of cultures and the use of 

 antitoxin, the death rate from the infectious diseases has 

 been sensibly diminished and the length of human life cor- 

 respondingly prolonged ; and this is notably true of Eng- 

 land, the country where the most careful attention has been 

 given to the subject and the greatest amount of money ex- 

 pended in its accomplishment. 



Public hygiene or preventive medicine, again, is like 

 agriculture in its method of dealing with those evils which, 

 on the one hand, destroy human beings and limit their 

 progress, and, on the other, those which seriously interfere 

 with the abundance and the quality of growing crops ; and 

 the principles of prevention which are applied in either case 

 are very much alike. 



If a sound, healthy infant, born of healthy parents, were 

 to be placed in a glass case, and fed with pure food which 

 had been freed from all germs of disease by due process of 

 sterilization, and were constantly supplied with pure air 

 which had also been sterilized ; if the water which it drank 

 were to be always pure spring water, and if in all other 

 points it were to be treated on perfectly healthful princi- 

 ples, such an infant would never die of measles or small-pox 

 or scarlet fever or typhoid fever or whooping-cough or 

 consumption. 



So, also, in agriculture, if an ai)ple tree or a peach tree 



