Page:Popular Science Monthly Volume 14.djvu/536

520 air will not convey the poison, although it is safe to say that the area of its diffusion by this means is very limited. Instances in which sewer-gas has been known to be the means of conveyance are numerous, but the cases were confined to one or more rooms directly communicating with the sewer, or to a limited part of a building. But the typhoid fever poison is not a gas. In such a shape we can not conceive that it will lie dormant in suitable soil, that it will undergo phases which so closely resemble germination and growth, or that it can be transmitted to long distances when given a proper vehicle. We have here a right to make a scientific use of the imagination. We can not imagine it a gas, but we can form an idea of it as an atom, a germ capable of preservation, growth, and infinite multiplication. It has never been seen; it may be that it will never be seen. In the physical sciences we project ourselves ideally into the midst of many things unseen, yet with perfect theoretical conviction in the reality of their existence.

In the group of cottages to which the epidemic was confined we observe a certain order in the arrangement of the infected buildings. A close examination of the plan is nearly sufficient to convince one that this order is not due to chance. Nor can we explain it by a conveyance of the disease-germs in the clothing of the inmates. We have in the exempt houses a sufficient warrant against this supposition. The inhabitants of the exempt houses, as the outbreak of the fever extended, assumed generously nearly all the care of the afflicted families. They were daily and nightly in attendance upon the sick, and in many cases assisted in washing the linen. If this were true of the inhabitants of the houses that were exempt from the scourge, we are nearly safe in excluding personal conveyance of the germs by those who inhabited houses showing a sequence of infection.

During my attendance upon several of the cases I repeatedly looked over the ground and studied the habits of the different families, but, I am ready to confess, without discovering the clew to the extension of the disease from the single focus in the person of Schmidt; that is, to discover a clew that would meet the demands of the scientific germ theory. However, I became convinced that if I were able to find some domestic arrangement or prevailing condition that linked the infected families together under a common liability to the disease, I should become master of the position. Such a connecting link I found in the water-supply of the different families. I did not make the discovery accidentally, but only as a result of a systematic investigation. In all researches of this kind I believe that it is rare that the truth is stumbled upon in the course of a careless search. If we do not exclude cause after cause in the course of the search, we are almost sure in the end to halt midway between two probable conclusions without being sure of either.

It is necessary to recall the fact that five houses, g, h, i, e, and d, were supplied with water from the well t—an open curb-well, loosely