PRESIDENT’S ADDRESS—SECTION H. 165 
kinds of disease referred to do not kill all they attack ; while 
they farther damage the constitutionally defective, and leave some 
of them to attain to reproductive ages still less fit for reproduction 
than they were born, they leave others in a damaged condition 
who were born sound. And lastly, while they are not seen to 
attack those of imperfect constitution alone, or even preferentially 
in any marked proportion, they do seize preferentially upon those 
who are weak merely from immaturity, and those who are 
weakened and depressed temporarily ; while, when they become 
epidemic, or when their causes are introduced to the body in 
special ways, they seem to attack the weak and the strong 
nearly indiscriminately. In short, although disease is inevitable, 
all diseases are not so, and if we may not choose our mode of death, 
yet we may exclude some modes. Weare rightly fixed, therefore, 
to prevent some diseases—we obey both instinct and reason 
therein ; and if the near limit of the attainable oblige us to set 
our aim not very high, a measure of success both proximate and 
remote is thereby rendered certain. 
I began by mentioning the problems which Sanitary Science 
seeks to elucidate: namely, the causation of disease, and the 
nature of the conditions which impair function, diminish vital 
efficiency, and so conduce to shorten the duration of life. The 
investigation is made by experiment; the results are found by 
induction. The experiment is performed without our active 
intervention, or is unplanned, the corpus vile being any body of 
men, and the conditions of experiment those under which they 
happen to live; the record of observation is the register of the 
facts of individual lives ; and when these individual observations 
are accurate enough and numerous enough, they may be classified, 
and the work of induction may be begun. The method of 
collecting ‘the observations may be indicated under three heads : 
first, enumeration of the people; secondly, record of their 
individual fertility ; thirdly, record of the individual duration of 
life among them. Under these are included many different 
details; and the register must be so framed as to facilitate 
combination of the several particulars into more or less broad 
classes, and bring them into comparison with foods, with soils, 
and with climates. Few enquiries are more complicated than 
this, which seeks to estimate the vitality of nations ; for trust- 
worthy conclusions can be drawn only trom the total phenomena, 
all of which are inter-dependent, and influence all the rest ; and 
perhaps few are more difficult, because many conditions which 
modify the import of individual observations, and some that are 
of wider effect, are but accidental, and alter from time to time. 
The general lines upon which such an investigation is planned 
should therefore be broad; and if this arrangement render 
conclusion uncertain at first, it must be remembered that the 
facts and their classification are both the more likely to be 
