THE STORY OF THE BACTERIA. 1 05 



terial diseases, it is evident at once that there 

 are two distinct classes of preventive measures : 

 first, those which must be arranged and en- 

 forced by the public authorities, such as 

 Health Boards and their officers ; and second, 

 those which depend upon the intelligence, 

 knowledge, and faithfulness of private indi- 

 viduals. It does not lie within the scope of 

 this little book to consider, except incidentally, 

 the measures which should be taken by the 

 authorities on the large scale, to ward off epi- 

 demics or to secure proper sanitary conditions 

 among the people. 



It is not, in fact, the great and sweeping 

 epidemics, dramatic and frightful as they are, 

 which carry off prematurely the largest num- 

 ber of people ; but it is the bacterial diseases 

 which we have constantly with us, and to which 

 we have become so accustomed that we do 

 not usually realize their vast importance, and 

 against which systematic and persistent cru- 

 sades on the part of the health authorities are 

 only occasionally and fitfully undertaken. 

 Among the bacterial diseases which are well 

 understood, the most important, in some re- 



