Among the infusoria, like the amoebae, each individual consists of a single mass of protoplasm, and not of a number of distinct cells; but the protoplasm is differentiated. Round the greater part of the animal it seems to be somewhat harder, so as to form a sort of skin, excepting at one place which is softer than the rest, serving for the ingress of food and the egress of egesta.

Instead of throwing out pseudopods, the body is either covered entirely with cilia or they are arranged round the mouth. Once it has entered by the mouth, the food finds its way all through the protoplasm of the body.

A contractile vesicle exists, which pulsates rhythmically.

Mode Of Experimentation

For the purpose of examining the action of drugs upon infusoria an infusion of hay is prepared some days previously. Two small pipettes are then made, which will deliver drops of equal size.

This is done by heating a piece of glass tubing in the middle, drawing it out, and cutting it across by a scratch with a triangular file (Fig. 10). With one of these a drop of hay-infusion is placed on the covering-glass, which is inverted on a Stricker's stage and examined. In order to ascertain the lethal strength of a drug, a drop of a solution of the poison of a definite strength is then mixed with it, and the infusoria are examined again after a certain time.

1 Manassein, Ueber die Dimensionen der Blutkorperchen unter verschiedenen Einflussen. Tubingen, 1872.

2 Prussak, Wiener Akad. Sitzungsber. Ivi., 1876 (Abth. 2), p. 13.

3 Brunton and Fayrer, Proc. Roy. Soc, February 1875, p. 271.

Fig. 10.   Diagram to show the way of making small pipettes

Fig. 10. - Diagram to show the way of making small pipettes.

If they continue moving, another experiment is made with a stronger solution; but if they have completely stopped, it is repeated with a weaker one until the solution is of such a strength that the movements become very slight and cease almost immediately after mixing, and cannot be restored by the addition of water. As the two drops of fluid were of equal size, the lethal strength of the solution is just one half of that which was last added. By repeating the experiments in exactly the same way with different drugs, their relative poisonous properties are ascertained.

Heat increases the rapidity both of the rhythmical contractions of the vesicle and of the ciliary motion and consequently of the movements from place to place of the infusoria. It seems as if the cilia were not equally affected by heat, those which produce a longitudinal movement appearing to be acted upon more quickly than those which cause a movement of rotation. Both kinds are first stimulated and then paralysed.

At temperatures between 25° and 30° C. the contractions of the vesicle are greatly quickened, and the animal moves with great rapidity in the longitudinal direction.

Between 30° and 35° its movements are still very rapid, but it seems to have lost the power of direction; all the cilia seem in full action, and the movements of the individual are determined simply by their anatomical arrangement.

Above 40° the cilia, which act longitudinally, appear to have stopped and the animal rotates, at first very rapidly, then slower and slower until all movements cease, and the protoplasm appears to become fluid; but when the heat is still further raised it coagulates.1

Cold lessens the quickness of the rhythmical contractions of the vesicle, of the ciliary motion and of the movements from place to place. Weak electrical currents first quicken the ciliary motion and cause movements of rotation, then swelling of the protoplasm, slower movements, and finally apparent solution of the protoplasm.

Moderate currents produce a tetanic contraction of the protoplasm and of the cilia, while the contractile vesicle is unaffected.

Strong currents cause liquefaction of the protoplasm.

Saline solutions appear rather, if we may say so, to alter the conditions under which the infusoria live than to affect the protoplasm itself. Strong solutions cause them to shrivel and then to swell up and become motionless. This effect appears to be due to the solution altering the quantity of water which the protoplasm contains.

1 Kossbach, 'Die rhythmischen Bewegungserscheinungen der einfachsten Organ-ismen,' Verh. d. Wurzburger physik. med Gesellsch. A.N.F., Bd. ii., Separat-Abdruck, S. 23. This work contains a number of exceedingly interesting and valuable observations on the subject.

Weaker saline solutions, on the contrary, quicken their movements, and, instead of causing them to shrivel, make them swell up at once. Chloride of sodium, chloride, bromide, and chlorate of potassium, as well as alum, all have this effect.

Acids in minute quantities cause contraction both of the body and of the vesicle. The ciliary motion is at first quickened and then retarded; the rate of contraction of the vesicle is at once diminished.

Moderate quantities cause coagulation of the protoplasm with swelling and liquefaction after death.

Strong acids at once destroy the protoplasm.

Alkalies in minute quantities cause swelling of the protoplasm, dilatation and slowness of the contractile vesicle.

Moderate quantities at once arrest the movements, cause liquefaction of the protoplasm, and destroy its differentiation, the contractile vesicles and vacuoles disappearing. They then cause swelling, and finally solution.

In large quantities they produce immediate liquefaction of the whole body.

Other drugs appear to affect the protoplasm itself, and arrest its movements without producing any apparent change in it.

The most active are chlorine, bromine, corrosive sublimate, iodine, permanganate of potassium, and creasote.

Quinine is much less powerful than these, though it is much more so than most other organic alkaloids. Strychnine has only one-fourth the power of quinine.

Cobra poison at first greatly quickens the movements of infusoria and then arrests them, causing just before death a contraction of the protoplasm, which then expands to its ordinary size.