Science.

Waikato Times, Volume XXI, Issue 1771, 10 November 1883, Page 6

Science.

Bt Db. Andrew Wilson, F.E.S.E., &o. Thkbe is an auitnalcule, averaging in diameter the one five-hundredth of an inch,, or thereabouts, found in stagnant pools, and called the Amcaba. The name of the animalcule is derived from the Greek for " change." In appearance it is a mere speck of living jelly, which is ever changing its form — ever flowing, so to speak, from one shape to another. The living matter wh«r«of the amoeba consists it called protoplasm. This substance closely resembles white ef egg (or albumen) in its chemical composition. It is the one substance which seems to ba inseparable from life ; or to put it more exactly, life ii nowhere known or heard of except as exhibited by some form, or other of " protoplasm." Whatever may be the relations of protoplasm to life— a topic I need not disouss here — this much is assured, that life, as we know it, seems to require protoplasm or albuminous matter for its exhibition and mere existence. Protoplasm, in this way, becomes truly the " clay of the potter," woven by the powers that be into the wondrously varied warp and woof of living beings. The Amoeba, then, is a protoplasm-speck. It takes in food particles by any part of its frame, and it appears capable of digesting them in any part of its body. There is no mouth, stomach, heart, breathing organs, or nervous system. Yet the animalcule lives, and lives as perfectly in its own simple way as the man. There seems, indeed, a wide gulf betwixt humanity and the Amoeba, but it is a gulf that is by no means impassable, when we consider that a oommunity of likeness (in the essential nature of their living parts) and a sameness of funotion (in respect of the actions of life) characterise this lower form of life and the sphere of human hopes sad fears. We Bh&U have to refer hereafter' to the Amoeba as a type of a considerable number of actions which the physiologist studies in man, and it will serve a good purpose if wo, therefore, bear the humble denizen of the pool, with its soft protoplasm body, clearly in mind. Every living being — animal or plant, monad or man — performs three great funotions in the course of its existence. The physiology of any animal or plant can be summed up in the expression, that the whole business of life, so to speak, cfinsists of three great processes, which include many minor processes within their limits. There is, firstly, the function of Ntitrition, whereby the animal or plant nourishes itself, digests food, and repairs its ever-recurring waste. Then, secondly, succeeds the process of Innervation or Relation. Through the exercise of this latter function, the living being brings itself into "relation" with the outer world by means of its nervous system. To the discussion of the functions of the nervous system, this second department of physiology is, therefore r devoted. But hosts of animals and plants die daily. Continually the units of a race perißh and drop into the grave. Hence a third function — that of Reproduction—renews the race, just as " nutrition " renews the individual. New animals and plants are thus brought into the world to take the place of their fellows that have succumbed in the battle of life. It is clear that whilst these three functions represeut the collective type of the animal or plant, there must be many subdivisions of each action or duty. For example, the function of nutrition includes every action through which the individual body maintains its place in the world. Under this single head what subjects fall to be considered ? The reply is — firstly, foods ; then digestion — itself a comprehensive topio ; then the blood, into which food is converted ; next circulation, which disti'ibutea the blood to all the tissues of the body ; and then comes excretion, or the getting rid of waßte matters. This latter duty is performed by lungs, skin, and kidneys, so that the single word excretion stands for and implies the functions of breathing, of the skin, and of the kidneys respectively. Jf the other two main functions of the body, the same remarks hold good. Each funotion is susceptible of division into a large number of lesser actions and details. The so-called " life," then, of a human being may, without any straining, either of physiological language, ideas, or facts, be described rather as a series of " lives," than as one life. And this latter contention becomes plainer when we reflect that in our blood, aa well as in other fluids of our frames, there are "cells" or minute living particles, which certainly possess a power of motion independent of the body of which they form part, and which also ex hibit a vitality that is not dependent upon the frame, through whose blood-vessels they perpetually travel. For our present purpose, however, it must suffice that we regard the varied processes and actions of the body as existing in a close unity which lies on the surface of things. Health and a truly enjoyable life are only possible to us when this unity is maintained. Derangement of one function is apt to oause aberration of many functions ; and we can only live a perfect and healthy life, physically, when every organ, part, and tissue co-oper-ates with its neighbors in the maintenance of the whole bodily existenoe. Our first consideration must be devoted to the consideration of the function of nutrition. It is only natural that we should first seek to know how our bodies are nourished. Why they are nourished we have already seen. Waste and wear are inseparable from existence. Every act of life means the wear and tear of the organ which works. Henoe, it is to repair and renew the perennial waste which the living body undergoes, that nutri- • tion devotes all its energies. The means whereby we repair waste are largely summed up in the words food and digestion. Food is the material from which we derive the new matter for living upon, and digestion is one word for many processes whereby this food is converted into a fluid capable of being added to and poured into the blood. Digestion, then, is merely the link which connects the food and the blood. Through digestion we convert food or matter that is more or lesg unlike ourselves into ourselves: The apparatus by which this action is effected is called the digestive system. Each collection of organs in a living body (the organs being devoted to th? performance of a funotion) is called a " system." Heart and bloodvessels form a "system" — thai of the circulation. Lungs, skin, and kidneys — forming a kind of natural trio — constitute the system of excretory organs, whioh are devoted to getting rid of waste matters. And in the digestive system, we find a whole series of organs which perform, each, an important part in the work of food-elaboration. Thus, there are the mouth and teeth ; then come the salivary glands of the mouth. The stomach and intestine come next, the food passing through these parts. The liver, " sweetbread" (or pancreas), gastric glands of the stomach, and the glands of the intestine are all so many organs whioh discharge dutiesconnected with the conversion of food into a fluid capable of being added to the blood; But last of all, it is possible to form a generalised idea of this complex system of digestive organs. ' We ought to think of any digestive system as merely a longer or shorter tube through which food passes, and in which food is subjected to the action of fluids thrown in upon it by certain glands (liver, sweetbread, <fee.) Suoh a simple idea — that of a tube with " glands """attached to its sides — perfectly describes the digestive system of 'any animaL—Knowledgc.