40 
Transactions Texas Academy of Science. 
life in recent years the following figures, taken from a verbal statement 
made by Professor Mansfield Merriman at the Boston meeting of the 
Society for the Promotion of Engineering Education, in 1898, are given. 
These were since published in the Proceedings of the Society. Professor 
Merriman stated that from investigations he had made he had found 
that the median age of man in 1850 was 18.6 years; in 1860 it was 19.3 
years; in 1870, 19.9 years; in 1880, 20.9 years; in 1890, 22 years; and 
in 1900 would probably be 23.1 years. By the median age is meant that 
the number of living persons younger than this age aquals the number 
living who are older. These figures strikingly exhibit the effect of edu- 
cation upon man’s condition, for since 1850 the median age has increased 
at an accelerated rate from 18.6 to 23.1 years — a gain of 4.5 years for 
every person living, or practically twenty-five per cent, of the median age 
in 1850. This gain has been brought about in the comparatively short 
space of fifty years, and is without doubt chiefly due to the revelations 
of modern science in exhibiting to us the causes of disease and the meas- 
ures to be taken for its prevention. Fifty years ago the engineering 
practices in sanitary science were crude in the extreme as compared to 
what they are now, and what was then done was largely by “rule of 
thumb” methods based upon very incomplete experience. 
Disease germs secure access to the human system in various ways, but 
the chief vehicles by means of which they accomplish this are water, 
milk, ice, contaminated food, air, dust, dirt, etc. Neither chemical nor 
microscopical examinations can always tell with certainty whether or not 
disease-producing organisms are present, but large quantities of organic 
matter or excessive numbers of micro-organisms are always to be 
regarded with suspicion, for along with much organic matter come the 
conditions favorable for their transmission, and with a large number of 
bacteria present it is likety that pathogenic ones may exist — at any rate 
the conditions are favorable for their growth and transmission. The 
bacteriologist may point out the presence of these microscopic organisms, 
but it remains the duty of the engineer to remove them before they find 
lodgment in the bodies of persons having weakened constitutions or 
physical conditions favorable for their rapid multiplication. Obviously, 
then, the engineer sustains an important relation to the public health — 
a more important one than most of our smaller cities seem to appreciate, 
if one may judge by a comparison of the salaries paid to engineers and 
those received by other officials. 
Water, more than any other medium, furnishes the readiest vehicle for 
the transmission of these disease-producing organisms, not only because 
the majoritjr of such organisms are water borne, but also because it is 
most copiously taken. Surface water is more likely to be contaminated 
than that drawn from wells and other underground sources, but unfor- 
