The movements of protoplasm are intimately connected with processes of oxidation going on in it.

By these processes chemical energy is converted into the mechanical energy exhibited in the movements, and this is sometimes very considerable.

The oxygen which takes part in these processes is not always derived from the surrounding medium at the exact moment when the movements take place; it may have been obtained some time before, and the movements may continue for a little while after all oxygen has been removed.

1 For further details see Physiological Chemistry, by A. Gamgee, vol. i., 1880, p. 130.. f 2

It therefore appears that protoplasm has the power of absorbing and storing up within itself, in some manner or other, oxygen, which it can afterwards utilise for the purpose of liberating mechanical energy.

This storage of oxygen takes place not only in the protoplasm of unicellular organism, but also in the tissues of the higher animals, e.g. the muscles.

The exact way in which storage occurs is not known, but it has been well compared by Professor Ludwig to the storage of oxygen in gunpowder. The oxygen is there contained in the nitrate of potassium, a compound which is readily decomposable by the application of heat, and then gives rise to the evolution of mechanical energy; and this it does perfectly well in an enclosed space, like a gun-barrel, where no air is present.

The power of storing up oxygen is very limited, and although protoplasmic movements continue for a little while after all external oxygen has been removed, yet they will not continue long.

A convenient way of ascertaining this fact has been devised by Kuhne, who adds a small quantity of blood or of haemoglobin solution to a drop of water containing protoplasmic organisms or cells placed on a covering-glass. This is then observed with a micro-spectroscope, The haemoglobin solution exhibits the two bands characteristic of oxy-haemoglobin. When all the oxygen is removed by means of a stream of hydrogen, kept up for some time, the spectrum of oxy-haemoglobin passes into that of reduced haemoglobin.

The occurrence of this change indicates the moment when all the oxygen has disappeared from the liquid. By reckoning from this moment onwards, we are able to estimate the length of time during which the movements continue in the absence of oxygen.

Oxygen-Carrying Power Of Protoplasm

Not only does protoplasm possess the power of taking up oxygen readily and assimilating it to itself, but it has also the power of taking up and giving off oxygen to other substances when these substances would be unable to take it themselves.

We may understand this action better by comparing it in a very rough way with that of a man whose greater strength enables him to seize fruit or break off pieces of sweatmeat and give them to his child, which thus enjoys what it could not have obtained for itself, however desirous of them it might be.

Method Of Experimenting

Guaiac resin, when finely divided and oxidised, becomes of a blue colour. It has, however, only a slight power of attracting oxygen to itself from the air, or from water in which the oxygen is dissolved, and thus the blue colour is developed slowly.

On the addition of protoplasm to the water containing the guaiac, the blue colour is developed rapidly. The reason of this possibly is, that the protoplasm has taken up oxygen from the water and given it over to the guaiac. This process reminds us of the action of spongy platinum in causing oxidation of hydrogen or formic acid.

Ozonising Power Of Protoplasm

It has been supposed that, in addition to its power of oxidising such substances as guaiac by giving to them oxygen which it has already taken up, protoplasm has the power of actually breaking up the molecules of oxygen and forming ozone.

The rapid oxidation which protoplasm causes has been attributed to this power. A similar action to this is observed during the slow oxidation of phosphorus. Phosphorus appears to break up the molecule of oxygen, taking to itself one atom and freeing another, which unites with two more in order to form ozone.

Action Of Drugs On Oxidation

A convenient way of testing the effect of drugs upon oxidation is to use the protoplasm of potato, of lettuce, or of dandelion. The most active part of the potato lies just under the skin, as is seen by pouring some freshly prepared tincture of guaiac over its cut surface. A ring of blue first forms close to the skin, and is always darkest there, although it may extend over the whole of the cut surface. The ammoniated tincture of the British Pharmacopoeia will not answer. The tincture must be made with spirit only. When potato is used, the whole of the potato may be pounded with water, or, still better, the peel alone may be cut off and rubbed up with water in a mortar and then filtered through linen. When lettuce or dandelion is used, the fresh leaves are triturated in a mortar with five or ten times their bulk of water, and the solution is then filtered. A row of test-tubes or test-glasses having been prepared, a measured quantity of water is put into the first. In this glass the protoplasm is not mixed with any foreign substance, and it therefore serves as the standard with which to compare the others; and into the others is put a similar quantity of solutions of the drugs to be tested. Each test-glass is distinguished by a label bearing either a number or the name of the drug which it contains attached to it. To each glass a measured quantity of the lettuce-water is added and the contents mixed by shaking. All are allowed to stand for a period varying from a few minutes to some hours. Then a small drop of freshly-prepared tincture of guaiac is added to each, mixed by shaking, and allowed to stand for one or two minutes; the glasses are then arranged in the order of depth of colour.

Fig. 11.   Test glasses for examining the action of drugs on oxidation

Fig. 11. - Test-glasses for examining the action of drugs on oxidation.

In this way it is found that many drugs greatly lessen or almost completely abolish the oxidising power of protoplasm, so that while the lettuce-water in the standard glass assumes a dark-blue colour, that in the others exhibits varying shades of blue, or may even retain the creamy-white colour caused by the guaiac without showing any blue whatever.

The colour is deeper and the reaction is more readily obtained when the tincture of guaiac is mixed with some substance capable of giving off oxygen readily, such as a solution of peroxide of hydrogen in ether, usually called ozonic ether.

A number of experiments made with potato-water by Cash and myself showed that oxidation in potato solution was diminished most powerfully by strychnine, then by quinine and coniine; next by morphine, codeine, cin-chonine, and atropine, each of which had almost exactly the same action; next by nicotine, and then veratrine. Aconitine seemed neither to retard nor accelerate oxidation, and presented exactly the same degree of coloration as the standard solution. Caffeine, picrotoxin, and digitalin appeared somewhat to hasten oxidation.1

Reduction By Protoplasm

Ehrlich2 has shown, in an interesting manner, the properties of oxidation and reduction possessed by protoplasm. Methylene-blue, alizarin-blue, and indo-phenol are coloured bodies which become colourless on being reduced. After injecting methylene-blue into the veins, he found that most of the parenchymatous tissues became coloured, the heart, brain, cortex of kidney, the voluntary muscles, etc, while the lungs and the liver were normal and only a small amount of colouring matter could be obtained by prolonged exposure to the air. Ehrlich concluded that the indifferent paraplasma of the cells excretes the unchanged matter, while the protoplasm, which is greedy for oxygen, excretes the reduced colouring stuff.