1. By feeding with chemically different foods very characteristic alterations are obtained, both in the colour reaction and morphology of the cell. For example, in five seconds white of egg causes both the cytoplasm and nuclear plasm to become more eosinophile, while pure amphopeptone increases their affinity for blue stains. The former food quickly causes great impoverishment of cytoplasm and nuclear plasm, while the first effects of pure peptone are to increase their bulk and density. Both the foods produce an enormous increase of the chromatin element of the nucleus, while other foods, e. g. nucleic and nucleic acid, produce no such result.
2. While the cytoplasm is the cell constituent most rapidly and most constantly affected by external stimuli, the nucleus is the seat of metabolic activity, and the state of the nuclear organs indicates whether or not the food supply was of service to the metabolism of the plant.
It is not surprising, therefore, to find a certain independence of cytoplasm and nucleus in their behaviour to external stimuli, coupled with great interdependence with respect to all resulting processes of metabolism. Thus, substances such as paraffin and nucleic acid act merely as stimuli to the secretive activity of the cells; and they cannot be regarded as foods, for they affect the nucleus only by causing a slight drainage on the nuclear plasm and nucleolus. If the stimulus is very transient the nucleus remains unaffected. On the other hand, with highly nutritious food like egg-albumin and peptone the nucleus is the seat of the greatest change, and the chromosomes, i. e. the nuclein, undergo an enormous. increase, independently of the state of the cytoplasm. With egg-albumin we do not get these great changes in the nuclear organs till the cell plasm is thoroughly exhausted, while in the case of 10 per cent, amphopeptone we get them while the cellcavity is full of cytoplasm.
In all cases the process of recuperation begins in the nucleus. The nuclear plasm first becomes abundant, and restoration of the cytoplasm begins in contact with the nucleus, and spreads thence to the remoter parts of the cell.
3. To answer the question, whether the rapidity with which changes occur depends on the ease with which substances are absorbed, we must deal only with such changes as are characteristic of foods. Changes that are produced also by mere contact with insoluble substances must not be taken account of.
Changes which are produced in five seconds are rapid, yet in this short space of time we get quite specific alterations for two foods so different in their diffusibility as egg-albumin and peptone. But then only the plasm is affected, that is that cell constituent which I have just shown to be most rapidly altered by external stimuli. Nuclear changes, e. g. the increase of chromatin, must depend for their rapidity on the constitution of the food, i. e. on the series of chemical changes the latter must undergo before it is converted into basophile chromatin. In the two cases just cited the length of time required to produce this change differs widely, being about twenty hours in the case of egg-albumin, while oue hour suffices for peptone ; and yet from the changes wrought in the cytoplasm in five seconds we might argue that both foods entered the cells with equal rapidity. We may conclude, then, that the rate of plasmic changes depends on the rate of absorption, but that the rapidity of nuclear changes is commensurate only with the digestibility of the food.
4. In determining the relation between cytological changes in the gland cells on the one hand, and the degree of irritability in the leaves calculated from their rate of closure on the other hand, cytoplasmic changes only constitute our legitimate criterion; for I have shown above that the cytoplasm is the cell constituent directly influenced by external stimuli, and that nuclear changes are the secondary results of metabolism. A careful comparison of the action of the substances applied to the tentacles proves that there is a constant concord between the rate of closure of the tentacles and the degree of vacuolation produced in the cytoplasm. The citation of a few cases will illustrate this :
Paraffin and nuclein caused no closure, and very slight and transient vacuolation.
Pure peptone caused very slow inbending, and no vacuolation for one or two hours.
White of egg and milk caused rapid bending and rapid vacuolation.
Fibrin caused slower closure and slower vacuolation.
Creatin did not induce bending of all of the tentacles to which it was applied; and those that closed did so with extreme slowness. The vacuolation was only transient.
Leucin sometimes, but not invariably, occasioned bending, and this was extremely slow. Vacuolation of short duration ensued.
Urea caused no bending, but killed the leaves. Being therefore a poison, its action should not be compared with that of the other stimulants named.
5. By bringing healthy cells into contact with the waste products, creatin, leucin, and urea, urea was found to act as a poison, creatin as a mild stimulus to movement, and leucin caused active secretion without much movement. These two substances, therefore, do not injure the leaves, and they seem to be of some nutritive value.
At a future time I may ascertain the effects of feeding with various carbohydrates, should the results obtained from preliminary experiments give promise that such an investigation would be of any value.
Effects of Sodium Azide on Sodium Fluxes in Frog Striated Muscle