TWENTY-NINTH ANNUAL MEETING. 83 
We may divide all natural waters into four classes : 
1. Rain-water. 
2. Surface-water, including streams and lakes. 
3. Ground-water, including wells. 
4. Deep water —water accumulated at considerable depth below the surface, 
such as artesian wells and springs. 
Water containing a large amount of dissolved substances is not considered 
good for public supply, yet a small amount is considered of value. The presence 
of substances which ordinarily exist in solution in natural water is not regarded 
as necessary, because experience has shown that distilled water, properly aerated, 
is perfectly wholesome. It is, however, true that a person who is in the habit 
of drinking soft water generally experiences some derangement of the digestive 
organs on beginning to use distilled water. It has also been proven that the sys- 
tem needs salts of lime for the development of the bones of the body, and that 
these salts exist in the water; consequently, distilled water would not be so bene- 
ficial to the human system as comparatively hard water would be. Surface-waters 
containing vegetable matter are unhealthy, causing diarrhea, and other diseases, 
such as malaria and fevers. The most dangerous effects are believed to come 
from waters polluted with waste materials from large dwellings or sewage of 
towns and cities. 
The ‘‘germ theory” of disease is that many diseases are due to the presence 
and propagation in the system of minute organisms, which are termed bacteria, 
and that some of the diseases which have their cause in such organisms are ma- 
larial fever, typhoid fever, diphtheria, and tuberculosis. Admitting the presence 
of these organisms in the bodies of persons sick with certain diseases —organ- 
isms which, at least in certain stages of their development, can exist outside the 
human body and retain their vitality for a long time —the question arises how 
they can find their way into the system of healthy persons to produce disease. 
The two most obvious of possible carriers of diseases are the air we breathe and 
the water we drink. Filtering cannot be relied upon in all cases. It has been 
known to fail utterly in the examination of the most contaminated reservoir 
water; even the best filters available will not keep back the smallest cell forms, 
sometimes very abundant. The small protococcus cells have been found in great 
numbers in waters filtered through sand, silica, or even filter paper. Fortu- 
nately, however, these forms are not common in waters. Professor Mallet, in: 
regard to his idea on disease, says: ms 
“If the theory be accepted which has so much in its favor, attributing the 
production of disease to organic matter in drinking-water — not to say specif- 
ically a poisonous substance or substances, but to the presence and actions of 
organic organisms —it seems quite conceivable that a water containing organic 
matter of any kind, including vegetable matter, may be harmless at one time, and 
harmful at another, when perhaps a different stage of fermentation or putrefac- 
tive change may have been entered upon and special organisms may have made 
their appearance or entered upon a new phase of existence. Thus, there might 
possibly be safety in drinking a peaty water, or water filtered through beds of 
dead forest leaves, when fresh; danger when, after a certain amount of atmos- 
pheric exposure, bacterial organisms had become developed; and safety again, 
perhaps, after the growth of such organisms had fallen off and more or less of the 
available organic matter had been consumed.” 
Though views may differ, we shall be safe in accepting the following summary 
as given in Nichols on ‘‘ Water-supply ”’: 
1. ‘‘A water suitable for domestic supply must be free from all substances 
