turbid, so that in this manner the mud will be caught in the bag on drawing it up to the surface.

In order to make the investigation a thorough one, a small portion of this muddy matter, which generally consists of decaying organic substances, is placed at once under the microscope, and the organisms contained in it are determined. Besides doing this, it is desirable to put a large quantity of the mud, say about one hundred grammes, into a glass jar, which can be closed, and to add some water from the well from which the mud was taken. Then this should be quietly set aside for two or three weeks, in some light spot, where the warm sunbeams can penetrate, so that any eggs or germs present in the water may be destroyed. In this way a great deal may yet be ascertained that could not have been learned at the examination conducted immediately after obtaining the sample.

"But what does the mud from such a well contain?" will be asked by the reader with whom the question what it is that he must guard against is of prime importance. This question is here to be answered. First of all, let a glance be cast at the woodcuts subjoined. Excepting Figs. 6, 7, and 8, the organisms represented are visible only under the microscope, or at least require, in order to be distinguishable, the aid of a powerful Fig. 1. magnifying lens. Nearly every particle of well-mud contains the amœbæ pictured in Fig. 1. They resemble drops of flowing liquid, and constantly change their form by sending out ray-like extensions. These extensions of the body are called pseudopodia, because their appearance creates the impression that the little animal is possessed of feet. But this is not the case; the pseudopodia (ps) are formed only in the moment when a change in location is desired, and they cease to exist when the place is reached which the little animal sought to attain. It can easily be proved that these amœbæ are animals, for they take up solid particles of food, digest the same, and cast out again whatever has not been assimilated. There is no vegetable organism which takes up solid particles into its interior for sustenance. The propagation of the amœba takes place in the simplest manner imaginable, by fission: a large specimen contracts at the center and ultimately divides into two parts, so that the mother-animal is actually rent into halves. In the body-substance of these beings, which are on the lowest plane of organic life, the microscope discloses a number of small particles, and a larger kernel (k), which is called the nucleus. Besides this there are yet one or more clear spaces called "vacuoles" (v). When fission takes place, the nucleus is also