Page:Popular Science Monthly Volume 8.djvu/706

686 , passes into the intestine, and, by means of its hooks and suckers, attaches itself to the intestinal walls, when it begins to grow with great rapidity, a length of many feet being attained in a few weeks. The part attached is the mother or head of the tænia, and until this is dislodged the worm goes on producing segments, or more properly proglottides, each of which is a perfect sexual being loaded with eggs. These are successively detached and escape with the evacuations, to be swallowed, perhaps, by some other pig, in whose flesh a new crop of cysticerci will soon develop. An egg of the Tœnia solium may be swallowed by a man instead of passing into the stomach of a pig. It is hatched in his stomach precisely in the same manner, and the embryo takes up Its lodging in some inclosed cavity. Some have been found in the eyeball, in the lobes of the brain, in the heart, and in the muscles. Whatever symptoms its presence may give rise to, it obviously has no chance for further progress, having selected the wrong vehicle to travel in. Man harbors not only the Tœnia solium, but another species very similar which naturalists have only learned to distinguish from it during the last few years, the Tœnia medio-canellata. Its cysticercus is found in beef, and is introduced when the meat is eaten in a raw or partially-cooked state. Tœnia nana and Tœnia lata are the names of other tapeworms inhabiting man, but both are limited in geographical distribution. The former is found only in Egypt, and the latter is confined to Russia, Poland, and Switzerland.

All these internal parasites, including the Trichina spiralis, which we have not space to speak of further, are introduced into the body either with the food or the drink, and a simple and effectual means of avoiding them is, to thoroughly cook the food and carefully purify the water.



ROFESSOR TYNDALL began his paper by alluding to a former inquiry on the decomposition of vapors, and the formation of actinic clouds, by light, whereby he was led to experiments on the floating matter of the air. He referred to the experiments of Schwann, Schroeder and Dusch, Schroeder himself, to those of the illustrious French chemist Pasteur, to the reasoning of Lister and its experimental demonstration, regarding the filtering power of the lungs; from all of which he had concluded, six years ago, that the power of developing life by the air and its power of scattering light 