PRESIDENTIAL ADDRESS.—SECTION I. 
(Sanitary Science and Hygiene). 
MEDICAL SCIENCE AND DISEASE PREVENTION, 
By JAMES JAMIESON, M.D. 
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Durine the last few years science in all its branches has made 
immense strides, and it may be safely said that medicine has 
not lagged behind. Hygiene, regarded as a department of 
medicine, has benefited freely by the progress made in the 
various sciences upon which its principles and practices must be 
based. No department of human knowledge can establish a 
claim to the name of a science until its practices are fairly based 
on something better than empirical observation, or on what is 
commonly called “rule of thumb.” It is still the case that 
doubts are thrown on any claim made by medicine to rank 
among the sciences, and even those who are most justly proud of 
its astonishing advances have to admit that they cannot supply 
scientific eround and reason for every point in their practice. 
But, at the same time, it may quite properly be claimed that 
much in medicine which was once empirical is now rational. In 
these days we cannot be content to remain at that empirical 
stage in any of the great subjects which occupy the attention of 
the physician and the medical sanitarian. Extended knowledge 
in chemistry, improved methods in physiology, and, where neces- 
Sary, experiments on animals have allowed such progress to be 
made that whole departments both of curative and preventive 
medicine can now be described as resting on a scientific basis. 
There are three diseases which are always with us, and 
the causation, prevention, and cure of which have received 
special attention of late years. These are typhoid, tuber- 
culosis, and diphtheria, about each of which much that is 
interesting and important has, in recent times, been 
elicited. F or some years there has been almost complete 
agreement among pathologists that diphtheria is a contagious 
disease, and that it owes its origin to a specific form of 
bacillus. Now, it is a characteristic of most, if not all, of 
the acute germ diseases, that after they have passed off the 
person so affected is protected against a further attack for a 
