PRESIDENT’S ADDRESS. 1029 
virulence to its action. Jnsanitary conditions also preduce 
depressing effects upon the human body and lower its powers of 
resistance. Germ-life possessed of this special virulence may 
attack the healthy, or the individual may fall a victim more by 
reason of loss of resistence than by the special activity of the 
microbe. These insanitary conditions then are essentially local, 
and although they exercise a considerable influence in the pro- 
duction of infectious diseases, it must be the duty of the local 
authority to deal with them. 
2. The sources of communicable diseases are in numerous 
instances not local but general, that is, they are not limited to the 
jurisdiction of one local authority but have relations to many. 
Water supplies are frequently in this sense general, food supplies 
are almost always so, and where infection extends from one person 
to another there is a general character in this source also, from 
the fact that facilities for travel and intercommunication are so 
easy and so numerous that diffusion rapidly takes place from 
one locality to another. In this respect communicable diseases 
must fail to be controlled by local authorities. Their manage- 
ment to be effective is clearly a function of a central power. 
3. The extreme readiness with which many infectious diseases 
may be diffused suggests at once the necessity of prompt action. 
But promptitude is not usually a characteristic of minor and 
isolated bodies in authority. Too frequently local considerations 
based on personal relations to the individuals affected paralyse 
action, and all the more certainly if several authorities are bound 
to co-operate. But delays are cruelly dangerous. The area of 
infection speedily enlarges and irretrievable mischief arises to the 
public health. It is evident if a combination of circumstances so 
directly tending to inaction are to be effectively controlled, then 
the authority must be central and not local. 
4. This efficient control likewise requires not only prompt 
administration but the collateral aid of a well equipped bacterio- 
logical laboratory. The work of this new department has become 
the basis of public hygiene, and at the same time a principal 
agency in the defence of the public health. Whatever researches 
of a theoretical nature bacteriologists may pursue, their labours 
in connection with the public health are essentially practical. A 
mere enumeration of these labours is at once sufticient to indicate 
their supreme importance in directing the practice of public 
hygiene, as well as to show the indispensible position to which 
they have attained in the management and control of infectious 
diseases. They may be set out somewhat as follows :— 
(a) The examination of ordinary products, such as food, water 
supplies, air, and soil. 
(6) The examination of the normal tissues, secretions, and 
excretions of the human body. 
