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in all animal fluids and most tissues, except bones, teeth, red blood corpuscles and red muscle.

Potassium Chloride commonly accompanies sodium chloride in small quantity. In the red blood corpuscles and in muscle it occurs in greater amount than the sodium salt, while in the blood plasma but little is found in comparison with the sodium salts, and any excess seems to act as a poison to the heart.

Carbonates and phosphates of calcium, sodium, potassium and magnesium occur in small quantities in most tissues. The earthy part of bone is chiefly composed of calcium and magnesium phosphate and calcium carbonate, together with some calcium fluoride.

Sulphates of sodium and potassium, probably formed in the body from the oxidization of the sulphur in the complex proteid materials, occur in most tissues, and are removed from the body by the kidneys.

Finally, we find two of the elements free in the textures. Of these Oxygen plays by far the most important part. It is widely distributed among the fluids of the body, from which it can be removed by reducing the pressure of oxygen of the atmosphere by means of an air pump. Oxygen is introduced into the body by the lungs, where the blood takes it from the air. In the blood only a small quantity of that which can be removed by the air pump is really free; the remainder is chemically combined with the coloring matter of the blood. It is absolutely necessary for life, as it alone can enable the chemical changes of the tissues, which are mostly oxidizations, to go on. It is, in fact, the element necessary for the slow combustion which takes place in the nutrient material after its assimilation.

Nitrogen also occurs in the blood, but in insignificant quantity. It is absorbed from the atmosphere as the blood passes through the lungs. So far as we know, it has no physiological importance in the body.

CHAPTER IV.

THE VITAL CHARACTERS OF ORGANISMS.

The manifestation of so-called vital phenomena in man forms the subject-matter of the following chapters, and some explanatory definition of the vital characters of the simpler organisms will be useful in preparing the beginner's mind for the more intricate questions in human physiology. This, with the foregoing short account of the chemical and structural peculiarities of animals, will complete a rough outline of the general character of organisms.

Protoplasm has already been referred to as the material capable of showing vital phenomena, the most obvious and striking of which are its movements.

Besides the common molecular or Brownian movement of the granules in protoplasm-which may be seen in most cases where fine granules are suspended in a less dense medium-protoplasm can perform motions of different kinds which must be regarded as distinctly vital in character. This movement may be said to be of three different kinds, according to the results produced, viz.: (1) The production of internal currents. (2) Changes in form. (3) Locomotion. In reality, the two latter are dependent on the first.

The existence of currents moving from one part of the protoplasm to another can be well seen in vegetable cells, when the cell wall restricts the more obvious change in form or place. Thus in the cells forming the hair on the stamens of Tradescantia Virginica the various currents can be seen in the layers of protoplasm which line the cell wall.

The granular particles course along in varying but definite directions, passing one another like foot passengers in a crowded street. The first and most obvious result of this is, that the different parts of the substance are frequently brought into contact with one another, and thus the products of any chemical

changes taking place at a given part of the cell body are rapidly distributed over the entire mass of the protoplasm.

The change in form occurs if there be no definite cell wall-as in naked vegetable spores and amoeboid forms of animal life-to restrict or direct the current of protoplasm; it flows unto various directions in bud-like processes, which appear at various parts of the protoplasmic mass, so as to cause a constant change in the form of the cell. These outstretched processes sometimes flow together and become fused, often enclosing some of the medium in which the creature is suspended, or catching some foreign particle floating near them.

FIG. 35.

A

B

The flowing out of these pseudopodia usually takes place for some time persistently from one side of the cell; and the body of the cell has to follow, as it were, the protrusion of the processes in such a manner that in a short time definite change in position or movement in a certain direction occurs: thus the protoplasmic unit may be said to perform definite progression or locomotion. All these movements may be seen in the white blood corpuscle of a cold-blooded animal, such as a frog, and still more easily in the unicellular amoba.

An amoeba figured at two different moments during movement, showing a clear outer layer and a more granular central portion. (n) Nucleus; (i) Ingested food. (Gegenbauer.)

Various influences may be seen to affect the rate of movements and probably influence at the same time the other activities of the protoplasm. Foremost among these must be named: (1) Temperature. If a protoplasmic unit, which is observed to be motile, be gently warmed, the movements become more and more active as the temperature is raised, up to a certain point, about 35°-42° C., when a spasm occurs, resulting in the withdrawal of the pseudopodia; soon after this the cell assumes a spherical shape. If the heat be carefully abstracted before it has attained too great a height, the protoplasm may recover and again commence its movements. If,

on the other hand, cold be applied to moving protoplasm, the motions become less and less active, and commonly cease at a temperature about or a little above 0° C. (2) Mechanical irritation also produces a marked effect on the movements of protoplasm. This may be well seen in the behavior of a living white cell of frog's blood under the microscope. It is spherical when first mounted, owing to the rough treatment it goes through while being placed on the glass slide and covered; shortly its movements become obvious by its change in form, which may again be checked by a sudden motion of the cover glass. (3) Electric shocks given by means of a rapidly-broken induced current cause spasm of the protoplasm, the cell becoming spherical. (4) Chemical stimuli also have a marked effect; carbonic acid causing the movements to cease, and a supply of oxygen making it active. The movements and other activities of protoplasm are, during life, frequently modified and controlled by nerve influence, as will appear in the following pages. This may readily be seen in the stellate pigment cells of the frog's skin, which can be made to contract into spheres by the stimulation of the nerves leading to the part.

The motions of protoplasm are thus seen to be affected by external influences, but the most careful observer cannot find physical explanations of the various movements which have been described. It is necessary, therefore, to ascribe this power of motion to some property inherent in the protoplasm, and hence the movements are called automatic. We are unable to follow the chemical processes upon which the activities of the protoplasm depend, and we therefore call them vital actions; but we must assume that these so-called vital properties depend on certain decompositions in the chemical constitution of the protoplasm. We know that some chemical changes take place, as we can find and estimate products which indicate a kind of combustion; but we know little or nothing of the details of the chemical process.

From the foregoing description of the manner in which protoplasm responds to external stimuli, it may be gathered that it is capable of appreciating impressions from without; indeed, it can

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be said to feel. We can only judge of the sensitiveness of any creature by the manner in which it responds to stimuli, and we may therefore conclude that the smallest particle of living protoplasm is endowed with definite sensitiveness: this must be noted as one of the most striking properties of protoplasm.

Every particle of living protoplasm has the power of assimilation. Taking into its structure any nutrient matters it meets with, by flowing around them in the way mentioned, it brings them into direct contact with differents parts of its protoplasmic substance. This nutrition of the cells gives rise to their growth, and finally leads to their reproduction. These facts will be more closely examined when speaking of their relation to cell life.

When a certain size has been attained, the cell does not further increase, but prepares to bring forth a cell unit similar to itself. This is spoken of as the reproduction of cells.

Different kinds of cell reproduction have been observed, which are all, however, modifications of the same general plan. The first is that by the formation of a bud from the side of the parent cell; this bud increases in size, and finally detaches itself from the parent and becomes a separate individual. This process, which is called gemmation, can readily be seen in all its stages in growing yeast, where the torula cells have various-sized buds