CUT No. 9. Bony Tissue. (Sharpey.) (A. E. Schäfer.) Let us see how the same kind of cells are planned to work together. Here is a group of ciliated cells, such as are found in the lungs, the nose, and certain other portions of the body. The little ciliae move in rhythm, first turning toward the fluid or solid to be pushed along, the one cell bringing it over to the second, the second to the third, until in perfect rhyme it is passed along. The same action is seen in the oesophagus and the intestines, where rhythmic muscle-motion, like the stripping of a hand in milking, passes the material along. (Fig. 10.) Still again we find the assemblage of different kinds of cells for a single specialized work. In the accompanying dia gram of a hair follicle, we see the hair, its root, the fatty tissue around it, the connective tissue, the little oil gland and the sweat gland, all united for a definite work. (Fig. 11.) In the next three pictures are shown the union cells of similar or different character in an organ; first, a cross section of the Thyroid Gland, then the Salivary Glands, and third, the wonderful Retina of the Eye, where over twenty layers of different cells are massed in the tiny, tissue-like layer on which the images of the eye impinge. (Figs. 12, 13, 14.) It is as if we had a regiment composed of white men and yellow men and black men; of large men and small men; of English, and French, and Italians, and Russians, and Indians, and Chinese, and Japanese, and Africans; of fat men and thin men; of tall men and short men, of all languages and races, yet, as one man, under the one general, obeying the one word of command. So we have in our body thousands of millions of cells of many different kinds, with varying functions, all under the mandate of one Ego, all inervated by nerve-telephone wires, whereby they act as a unit in the great machine. The Nervous System. We give a diagram of the spinal cord and the brain, together with cross-sections of the spinal cord. (Figs. 15, 16, 17.) If we consider the evolution of the brain, we shall find that it is really the spinal cord turned in upon itself, after the fashion of a cockle-shell wound around in a spiral. Looking at the cross-section (Fig. 21), the dark gray matter is shown in the margin, and the white matter, really the fibres of the brain cells, is in the centre. In the very centre is seen the hollow canal which runs all through the spinal cord. Looking again at the spiral and keeping in mind that it represents the spinal cord as seen at the cross-section, one can readily understand how the gray matter will be found on the surface or cortex and in the interior. All the white matter will be found therefore, in layers around the hollows formed by the division of the canal in the brain. As a matter of fact, germs can travel in the fluid of the canal from the lowest portion of the spinal cord to the centre of the brain. CUT No. 18. The Evolution of |