" Although the problem appeared difficult, I went " even confidently to the work. I wrote immediately: " to Herr Locher, in'Sigmaringen, and asked him for a " little foul-brood. The 18th of June I received, " enclosed in a letter, so much as I could form into a " ball about the size of a pea. The substance was very " dark, nearly black, moist, and tenacious, and its odour " was exceedingly disagreeable. A careful examination " under the microscope proved the presence of fungus " of the same form as Microoccus. Had I, after " having solved my problem, began first to show that " the spores could escape through the fly-holes (entrances) " of hives containing foul-brood, it would have been " necessary for me (in order to have obtained such a " hive) to dissolve the infectious substance in water, and " therewith sprinkle a comb containing healthy brood. " It is most probable that such a proceeding would have " failed, as the Bees would most surely have cast out " the dead larvae and pupae before the artificially pro- " duced sickness had had time to develop itself fully, " and infect the whole hive. In every case there would " have gone a much longer time by that means before I " had arrived at the result. I had not, however, in the " meantime the opportunity, as I already wished to " discuss my experiment at Halle. I, therefore, immediately made the experiment to catch the spores " that were escaping, and were floating in the atmo- " sphere, from the infected substance that had been sent " me, and thereafter use them for infecting healthy brood. " For this purpose I constructed the following appara- " tus : On a smooth-planed board I placed a bell-glass,* [185] "in the top of which was a round hole ; in this I fixed "a glass tube 2 feet long ; there was also fixed a "similar glass tube in the board. In the top of the " uppermost tube was fixed a plug of cotton-wool, as "also in the under end of the bottom tube, and the "wood was not pressed tight, but so that the air could "circulate freely through both tubes. The foul-brood "substance that I had received from Herr Locher, was "now placed under the bell-glass on the 21st of June, "and left to dry slowly. If, then, the assertion that the "spores escaped in the air when the substance was dry "was correct, then it was only necessary for me now and "then to place the apparatus by the window in my "study, and expose it to the full influence of the sun- "beams, as if the air in the bell-glass, by the power of "the sunbeams, was warmed up to 40\({}^{\circ}\), it must, by "a well-known physical law, escape through the upper- "most tube, while the cooler air from the floor of the "study must enter the bell-glass through the bottom "tube, and at the same time it was quite as certain that "therewithal the spores of the fungus, that were carried "by the upward current of air, would be caught in the " wool above." On the 5th July, on which day the substance was "quite dry, until the end of the month, I got four plugs "of wool, each of which had served as the top plug for "about eight days ; besides these I had two pads of " wool, each of an area of about 4 square inches, "which I had placed inside at the top of the bell- "glass." Had the spores from the substance really been " escaping? and had the wool caught them as they were coming out into the world? All rested on the "answering of these questions; and examination gave " the following results:--