April 19, 1894] 



NATURE 



587 



simpler instance, the tensions which allow the capsule of Im- 

 patiens to burst or the stamens of Parietaria to explode, are the 

 product of vilal activity, and have, moreover, an adaptive 

 quality. But the release is purely mechanical ; there is nothing; 

 Vi\it peire/iliott in the ordinary sense of the word, so that these 

 phenomena differ from the reaction of Mimosa. Pfeffer, 

 therefore, prefers not to consider the explosions of Miaiulus, 

 Parietaria, &c. as cases of irritability, while he acknowledges 

 that there is no real objection to the word irritability having a 

 wide enough meaning to embrace such cases. All that matters 

 is that we should have a clear conception of the existence and 

 importance of release action in the vegetable organism. Pfeffer 

 points out that in his " Physiology "' (iS8i) he laid down the same 

 general principles that are developed in the present address, to- 

 gether with examples in various regions of change, and that 

 even earlier, in his " Osmotische Untersuchungen " (1877), he 

 expressed, without reserve, the same views as applicable to the 

 phenomena of life generally. He claims for these views a prac- 

 tical priority in botanical literature, although he fully recognises 

 that Dutrochet, in 1S32, set forth perfectly clear and sound 

 views on the subject. 



In 1881, too, he used the word Reiz, i.e. stimulus-effect, as 

 equivalent to physiological release-action ; and he used the 

 expression Jit'lease intentionally, because of the mystic con- 

 ception attaching to the terms stimulus and irritability. In fact, 

 he would at the present moment throw over altogether the word 

 /\eiz if it were not that the time has gone by for those 

 mystic conceptions of life which are inconsistent with the law of 

 the conservation of energy. 



Pfeffer goes on to point out that when, in 1882, Sachs set 

 forth his belief in the general existence of irritability, and in its 

 necessity for the machinery of the organism, he spoke of it not 

 as a phenomenon in the wider category of release-actions in 

 general, but as a specific peculiarity of living organisms. Sachs, 

 according to Pfeffer, holds the- specific character of irritable 

 organs to be not so much their unstable equilibrium as the fact, 

 that after stimulation they return automatically to the labile con- 

 dition. Pfeffer claims that this definition does not apply to 

 many undoubted cases of stimulation. When callus is produced 

 by injury, or when adventitious roots are developed in response 

 to certain stimuli, there is no such automatic return, but a 

 permanent alteration. 



To produce a stimulus reaction, a change in external or in 

 inner conditions is necessary. The sensitive-plant does not 

 react to steady pressure, but to variation in pressure. An 

 analogous state of things is found when a plant in a condition 

 of cold-rigor is made to grow by heat. For the change in 

 temperature is merely a stimulus, since it only releases activities 

 which are carried on by the energy at the plant's disposition, 

 not by the heat. At a constant temperature the plant is in a 

 statical condition of irritability, which is a necessary condition 

 for the realisation of vital activity. If the results of tempera- 

 ture-changes are not generally recognised by botanists as pheno- 

 mena of stimulation, this is only a proof of the need of accu- 

 rate conceptions in this branch of physiology. The association 

 of the word with strikingly visible phenomena is partly to 

 blame for this. Everyone recognises that, for instance, in the 

 opening of the crocus or tulip flower, the change of tempera- 

 ature is a stimulus. In these instances the action of heat may 

 be compared to the regulation of certain machines of human 

 construction by the heat-expansion of a metallic rod. 



Even when the increased temperature, by increasing molecular 

 action, brings about a union with oxygen, still the temperature- 

 change is only the indirect cause of the combustion ; and this 

 reasoning applies to respiration. 



In a similar sense the addition of a salt of potassium to a 

 culture-fluid produces a release action in a plant in which 

 growth was checked by the absence of this element. 



Pfeffer has some interesting remarks on the condition of 

 irritability of organs in a condition of equilibrium : for instance, 

 on the continued action of the gravitation stimulus on a 

 geotropic organ growing vertically. Bacteria are less sensitive 

 to the attraction of meat-extract when themselves immersed in 

 dilute extract ; that is to say, the homogeneous medium, which 

 has no directive action, shows its effect in diminished irritability. 

 The same is true of heat, which stimulates when it varies, and 

 which, when constant, is a necessary condition for certain states 

 of irritability. The idea is not a new one, for no less a man 

 than Johannes Miiller (Pfeffer points out) defined the formal 

 conditions of animal and plant life as Lebensreize or integrirende 

 Reize. 



NO. 1277, VOL. 49] 



The stimulus need not come from the outside, for just as a 

 clock by internal machinery strikes at intervals, so in the 

 organism combinations occur which function as stimuli for cer- 

 tain effects. These are naturally obscure, and for this reason we 

 do well to fix our attention principally on external stimulation; 

 but it can hardly be too much impressed on us that the de- 

 velopment and ordered activity of the living body is 

 inconceivable without the co-operation of stimulus from the 

 inside. 



With regard to stimulus and reaction, we are in the position 

 of a man, ignorant of mechanics, who sets a machine in motion 

 by a touch of his finger, and who has no idea whether the 

 effect is due to a falling weight, to water-power, or to steam. 

 Considerations of this sort make us realise our ignorance, so 

 that when a new result is observed (in a case of stimulation) we 

 do not even know whether the cause is to be sought in 

 the perception of the stimulus or in the machinery of reply. 

 While denying himself the discussion of cognate points, 

 Pfeffer finds room to call attention to one or two interesting 

 points of resemblance in the irrii ability of plants and animals. 

 Thus, for instance, in plants as in man, an increase in the 

 stimulus produces a dulling of sensitiveness. Just as a beggar 

 is stimulated by the gift of a shilling, which on a rich man has 

 no such effect, so a starving bacterium is stimulated to move- 

 ment by excessively minute quantities of meat extract, while 

 the same organism living in the midst of plenty can only be 

 stimulated to similar movement by an absolutely greater quantity 

 of extract. In the irritability of plants we find, in fact, the 

 relations which are expressed in Weber's law — a proof that the 

 relation in question has nothing to do with the higher psychic 

 functions. 



A plant or a plant-organ is never sensitive to a single stimulus 

 only ; thus during a geotropic curvature mechanical traction 

 may bring about a strengthening of cell walls, and an injury 

 may produce protoplasmic movement. Here lies a proof that 

 different stimuli do not produce one and the same effect in a 

 given cell, that, in fact, the cell does not react like our eyes, in 

 which the most varied stimuli produce the effect of light. In 

 the case of plants there can be no question of such a limited 

 capacity — -of specific energies in the sense of Johannes Miiller. 



The development of distinct organs of sense whose function 

 is the perception of a single agent, is well known to be as little 

 characteristic of plants as of the lower forms of animal life. 

 But distinct organs of sense are no more a condition of irrita- 

 bility than they are of life. Indeed, plants exhibit a variety 

 of sensibilities equal to that of animals, while in delicacy of 

 perception the vegetable kingdom has the advantages. Bacteria 

 are attracted by a billionth or trillionth of a milligram of 

 meat-extract or of oxygen, infinitesimal quantities which we 

 cannot weigh, and of which indeed we cannot form any adequate 

 conception. It is just because the whole secret of life is con- 

 tained in protoplasm, that the simplest organism, such as a 

 bacterium, can be the theatre of as rich and varied a play of 

 stimulus and reaction as the most complicated plant. 



CHEMISTRY IN RELATION TO PHARMACO- 

 THERAPEUTICS AND MATERIA MEDIC A. 



["D Y the courtesy of the editor of the Lancet we are able to 

 L '-^ give the following translation of an address delivered at 

 the Eleventh International Medical Congress, by Prof. B. J. 

 Stokvis of Amsterdam University.] 



The Term and Scope of Pharmaco- Therapeutics. 



"Therapy "or "therapeutics," by which terms we under- 

 stand the art of serving the cause of humanity by assuaging 

 human suffering and healing human ill, avails itself of every 

 means in its power to arrive at these end-; ; elle prend son bien oh 

 elk letrouve. And the art of therapeutics, like all of us here 

 assembled at this Eleventh International Medical Congress, 

 has discovered that all ways lead to Rome. To Rome thera- 

 peutics has come — now in the guise of electricity, now as a water 

 cure, now as psychical influence ; so that we here are able to 

 review, as they defile like armies before us, electro-therapy, 

 pneumo-therapy, hydro-therapy, hypnopsis, and psychic sugges- 

 tion, and compare their merits as healing agents when 

 placing themselves at our orders to combat disease and 

 put death to flight. But most ancient of all the branches 

 of medical art is that w hich makes use of drugs ; and in 



