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Transactions Texas Academy of Science. 
ilance if we are to hope for anything like success. One hundred years 
ago Malthus made the assertion that “Diseases have been generally con- 
sidered the inevitable inflictions of Providence,” and Cruden, in his 
“Concordance” to the Bible, published near the middle of the 18th cen- 
tury, states that “Disease and death are the consequence and effect of 
sin.” He further states that the scriptures go to show that sometimes 
the visitations of disease were ascribed to Divine vengeance and some- 
times to the workings of the devil. These ideas were accepted in a gen- 
eral way until a comparatively few years ago, but in the light of modern 
investigations we know that disease is just as subject to natural law as 
are other natural phenomena, and that once having sought and found the 
cause of any specific disease it is possible to guard against infection and 
to treat more rationally the cases that actually occur. 
Although Jenner, in 1796, was the first to provide, by vaccination, a 
measure for the prevention of smallpox it is obvious that general meth- 
ods for the prevention of all manner of contagious or infectious diseases 
could not have been provided in advance of the discovery of the specific 
causes producing them. It was not until recent years that proof was 
found which showed that all such diseases were due to pathogenic bac- 
teria which secure access to the human system by contact with a source 
of infection, or in the air we breathe, the food we eat, or the water we 
drink. Almost daily the list of infectious or contagious diseases is 
increased through the discovery of their specific bacteria, and many dis- 
eases — such as malaria and intermittent fever — that were not formerly 
supposed to belong to this class are now known to do so. Sanitary 
science has grown along with the science of bacteriology and the last ten 
or fifteen years have witnessed the discovery of the greater part of what 
is now~ known in this line. Sanitary engineering, however, existed at an 
earlier date, for experience having taught that certain diseases occurred 
in conjunction with certain other conditions, such as the presence of 
decaying organic matter, man learned to provide measures for the 
removal of the causes, or supposed causes, from proximity to his habita- 
tions. 
The investigations of Pasteur led to the “germ” or zymotic theory of 
disease, while Koch's more recent work in bacteriology has converted the 
zymotic (or ferment) into the zymo toxic (or ferment poison) theory, 
which teaches that it is the poisonous products of the germs, rather than 
the germs themselves, that produce disease. But it matters little to the 
engineer how the germ does its deadly work, it is sufficient to know that 
the presence of certain germs leads to certain results, and that by exclud- 
ing them form the media by means of which they gain access to the 
human system infection may be avoided. 
The census reports of the United States show that about forty per 
