HANDBOOK OF PHYSIOLOGY.

CHAPTER 1.

THE PHENOMENA OF LIFE.

HUMAN physiology is that part of animal physiology which treats of man-of the way in which he lives and moves and has his being. It teaches how man is begotten and born; how he attains maturity, and how he dies.

As, however, man is a member of the animal kingdom, although separated and specialised no doubt to a remarkable degree, he during life manifests certain characteristics-possesses certain properties and performs certain functions-in common with all living animals, even the very lowest, and these may be called essentials of animal life. If we go a step further we find that most of these characteristic properties and functions are possessed also by the very lowest vegetable structures, and are in fact the characters by which we distinguish living from not-living matter; they are essentials or phenomena of life in general. Thus we see that as human physiology, which treats of man only, is a part of animal physiology, which treats of the functions and organisation of animals in general, so is animal physiology but a part of the wider science of Biology, which embraces the organisation and manifestations of all living things.

Before entering upon the study of Human physiology, therefore, it is useful and even necessary to devote our attention for a little while to the investigation of what are the properties and functions common to all living matter, and how they are manifested, since it would be unwise to attempt to comprehend the working of the complex machine of the life of man without some knowledge of the motive power in its simplest form.

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Living matter, in its most elementary form, is found to consist of a jelly-like substance which is now generally known under the name of Protoplasm.

This substance, in its most primitive form, and in minute masses, is found undifferentiated and perfectly homogeneous, and constitutes the lowest types both of animal and vegetable life that can be observed under the microscope. It is this substance, too, which forms the cells, of which even the most complex organism has been proved to be made up and from which it has been developed. Thus, the human body can be shown by dissection to consist of various dissimilar parts, bones, muscles, brain, heart, lungs, intestines, &c., and these on more minute examination are found to be composed of different tissues, such as epithelial, connective, nervous, muscular, and the like. Each of these tissues is made up of cells or of their altered equivalents. Again, we are taught by Embryology, the science which treats of the growth and structure of organisms from their first coming into being, that the human body, made up of all these dissimilar structures, commenced its life as a minute cell or ovum about th of an inch in diameter, consisting of a spherical mass of protoplasm in the midst of which was contained a smaller spherical body or germinal vesicle. The phenomena of life then are exhibited in cells, whether existing alone or developed into the organs and tissues of animals and plants. It must be at once evident, therefore, that a correct knowledge of the nature and activities of the cell, forms the very foundation of physiology.

Cells are, in fact, physiological no less than morphological units.

The prime importance of the cell as an element of structure was first established by the researches of Schleiden, and his conclusions, drawn from the study of vegetable histology, were at once extended by Schwann to the animal kingdom. The earlier observers defined a cell as a more or less spherical body limited by a membrane, and containing a smaller body termed a nucleus, which in its turn encloses one or more nucleoli. Such a definition applied admirably to most vegetable cells, but the more extended investigation of animal tissues soon showed that in many cases no limiting membrane or cell-wall could be demonstrated.

The presence or absence of a cell-wall, therefore, was now regarded as quite a secondary matter, while at the same time the cell-substance came gradually to be recognised as of primary importance. Many of the lower forms of animal life, e.g., the Rhizopoda, were found to consist almost entirely of matter very similar in appearance and chemical composition to the cell-substance of higher forms: and this from its chemical resemblance to flesh was termed Sarcode by Dujardin. When recognised in vegetable

cells it was called Protoplasm by Mulder, while Remak applied the same name to the substance of animal cells. As the presumed formative matter in animal tissues it was termed Blastema, and in the belief that, wherever found, it alone of all substances has to do with generation and nutrition, Beale has named it Germinal matter or Bioplasm. Of these terms the one most in vogue at the present day, as we have already said, is Protoplasm, and inasmuch as all life, both in the animal and vegetable kingdoms, is associated with protoplasm, we are justified in describing it, with Huxley, as the "physical basis of life," or simply "living matter."

A cell may now be defined as a nucleated mass of protoplasm,* of microscopic size, which possesses sufficient individuality to have a life-history of its own. Each cell goes through the same cycle of changes as the whole organism, though doubtless in a much shorter time. Beginning with its origin from some preexisting cell, it grows, produces other cells, and finally dies. It is true that several lower forms of life consist of non-nucleated protoplasm, but the above definition holds good for all the higher plants and animals.

Hence a summary of the manifestations of cell life is really an account of the vital activities of protoplasm.

Protoplasm.-Physically, protoplasm is viscid, varying from a semi-fluid to a strongly coherent consistency. Chemically, living protoplasm is an extremely unstable albuminoid substance, insoluble in water. It is neutral or weakly alkaline in reaction. It undergoes heat stiffening or coagulation at about 130° F. (54.5° C.), and hence no organism can live when its own temperature is raised beyond this point.

Many, of course, can exist for a time in a much hotter atmosphere, since they possess the means of regulating their own temperature.

Besides the coagulation produced by heat, protoplasm is coagulated and therefore killed by all the reagents which produce this change in albumen (see Appendix). If protoplasm be subjected to chemical analysis, the chief substances of which it is found to consist belong to the class of bodies called Proteids or albumins. These are bodies made up of the chemical elements C. H. N. O. and S., in certain slightly varying proportions. They are essential to the formation of protoplasm, for

In the human body the cells range from the red blood-cell (in.) to the ganglion-cell (in.).