We now come to the much more important question as to whether organic particles, bacteria, can pass through the trap. A simple but crude method of examining the question consists of a microscopical comparison of water through which soil pipe air has been drawn, with water through which air over the trap has been drawn. No particles were found, by this method, to have passed through the trap. The organic particles are rendered so heavy by soaking with water that they are neither raised with the aqueous vapor nor by wind blowing over the surface, as has been proved by Dr. Frankland and many others. But "marshes and swamps, in a dry season, when the water is low and the particles are drying on the muddy sides, and on the vegetation on the banks, are frequently very pestilential." Mr. Baldwin Latham says: "One thing is certain, with reference to malaria, that all authorities are agreed, that it is never extricated from a water surface." Dr. Car-michael set to work to prove these matters conclusively. He used a "culture" liquid capable of cultivating any germs added to it, and after sterilizing it in a temperature over 2120 F. he introduced into it the air taken from the trap to be tested. If after keeping the liquid at cultivation temperature, say from 60 to 120 deg. Fahr., for several weeks, it remains clear, then, no germs could have been in the air, and the water seal must have prevented their passage. If, on the other hand, the air had germs in it, they would multiply enormously in the infusion, rendering it opaque and perhaps producing growths of fungi.

The apparatus used is shown in Fig. 42. A glass flask containing the culture solution, a hay infusion, was connected on the one side with a U-shaped glass trap containing water, and on the other with an aspirator as shown. The hay infusion and the water in the U-shaped trap were both sterilized by boiling. The U-shaped trap was connected on its other side with the soil pipe side of the watercloset trap. It will be seen from this arrangement that any germs coming from the soil pipe which passed through the water trap would be carried in the air current over to the infusion and would cause it to putrefy. But no such particles passed through the trap seal, for the hay infusion remained perfectly clear though the experiments were continued for five months. The tests were made both with and without the aspirator, and various kinds of culture liquids were used. Tests were also made with the U-shaped trap omitted, and in these cases the infusions began to putrefy in a few days, showing that the water trap really prevented the germs from passing.

Fig. 42. Apparatus for determining: whether bacteria can pass

Fig. 42. Apparatus for determining: whether bacteria can pass through water in a trap.

These experiments seemed conclusive; but lest it might be objected that germs might rise from the liquid of the trap and fail to be carried over, or that an ordinary water-closet trap might behave differently from the glass one employed, Dr. Carmichael made a still more crucial series of tests as follows: Nitrogen bulbs, Figs. 39 and 43, were charged with a strong cultivating liquid called Pasteur's solution, and sterilized. The lead W. C. trap, connected with the soil pipe, was also sterilized by heating it to 350 to 400 degrees Fahr., and the bulbs were connected with the house side of the trap with an air-tight connection already described in connection with the first experiments. The other end of the bulb vessel was connected with the aspirator. In order to let air into the trap chamber above the water seal a filtering tube was used so that no germs could come to the bulbs unless they passed over the W. C. trap seal. The whole apparatus was most carefully and thoroughly sterilized. The filtered air was drawn by the aspirator into the chamber over the trap seal and then bubbled continuously through the liquid in the bulbs for from 24 to 36 hours, and the bulbs were then allowed to stand in a warm room at 75 to 100 degrees Fahr. for several months, and the experiments were repeated in the most rigorous and careful manner. The liquids in all the tubes and flasks, though kept for from two to five months at cultivation temperature, remained perfectly clear, and even when examined with a most powerful microscope used for germ studies and multiplying 900 diameters, exhibited no trace of life. Dr. Carmichael concludes as follows:

Fig. 43. Apparatus for determining more critically whether bacteria

Fig. 43. Apparatus for determining more critically whether bacteria can pass through water in traps.

"Water traps are, therefore, for the purpose for which they are employed, that is, for the exclusion from houses of injurious substances contained in the soil pipe, perfectly trustworthy. They exclude the soil pipe atmosphere to such an extent, that what escapes through the water is so little in amount, and so purified by filtration, as to be perfectly harmless; and they exclude entirely all germs and particles, including, without doubt, the specific germs or contagia of disease, which, we have already seen, are, so far as known, distinctly particulate."

Dr. Carmichael, in describing the pan closet used in his experiments, Fig. 43, says: "If you examine such a trunk (receiver) as is found in almost every house in Glasgow, you will find it coated over, to the thickness, frequently, of an inch or more with filth." He then recommended the short hopper he showed in the picture above the pan closet.

The two glass vessels shown in the initial cut to this chapter, illustrate another experiment made by Dr. Carmichael, to see if germs would rise from the surface of water at rest. He placed cultivating liquid in each of the tubes and connected them together at the top by a rubber tube. Into each tube had been placed a small capillary tube filled with a putrid liquid and hermetically sealed at both ends. The cultivating liquid was sterilized in both large tubes. Then one of the small capillary tubes was broken by shaking and its putrid contents thus mixed with the infusion in its enclosing vessel. The germs did not pass over into the other vessel, even though the test was continued for five years uninterruptedly.

Fig. 44. Apparatus for determining whether bacteria can escape

Fig. 44. Apparatus for determining whether bacteria can escape from a liquid at rest.

Fig. 45. Apparatus for determining if a current of air can take up

Fig. 45. Apparatus for determining if a current of air can take up germs from a liquid at rest.