the truly parasitic Entamoeba histolytica, which cannot live without invading the tissues, can be checked in this invasion and eliminated from the body by administering emetine, while other Entamoebæ, which live on fæcal debris, remain unharmed. Whether the tissues are so altered that the amœbæ cannot invade them, or the amoeba, without being directly killed, are so weakened in virulence that they cannot invade the tissue and obtain their food, but succumb in face of the normal resisting powers of the host, are possibilities on which we can only speculate, and no method of bringing them to the test of experiment has yet been found.

The work of Morgenroth and his co-workers, extending now over more than a decade, has again led them to emphasise, in connection with the curative action of substances which they have examined, a fixation to the cells and tissues of the host, a definitely organotropic property, as an important factor in the effect. Two examples may be mentioned.

V. Quinine and Malaria.

One of the earliest of chemotherapeutic discoveries, that of the cure of malaria by quinine, had never been satisfactorily explained. There was no evidence establishing even a probability that quinine, in such concentrations as can be tolerated in the blood of the living subject, would directly kill the malarial plasmodia, especially if these were partly screened from its action by their position in the interior of the red corpuscles. Morgenroth, from the results of his determinations by biological methods of the distribution of quinine in blood, is led to the conception of quinine as acting on malaria, in virtue of its fixation by the red corpuscles, either killing the trophozoites in their interior, or blocking the entry into them of the merozoites of the asexual cycle. On this latter supposition, it will be seen that quinine would act, not by killing the malarial parasites, but by rendering the blood unfitted for their multiplication. They are supposed to fall a prey to the natural defensive substances in the plasma, because a film of quinine denies them access to the red corpuscles, in the interior of which they could continue their development in safety. There are discrepancies between Morgenroth's determinations of the distribution of quinine in favour of the red corpuscles, and those obtained by direct chemical means, which would still need to be reconciled before either theory of the curative process in malaria could be fully accepted. Meanwhile, these suggestions are of interest as another example of the need found, more and more, by workers in this field to regard an organotropic property of a drug not as detrimental to its curative action but as an essential factor in the chemotherapeutic process.

VI. Remedies for Bacterial Infections.

This same property, of fixing themselves to the red blood corpuscles or to the connective tissue, has been observed by Morgenroth and his coworkers with the higher homologues of quinine, ethylhydrocupreine ('optochin') and octylhydrocupreine (' vuzin'), and with the dyes of the acridine series, with which they have obtained promising results in the treatment of bacterial infections. In the treatment of pneumococcus infections by optochin several factors, other than those of immediately

lethal action of the alkaloid on the pneumococci, appear to be concerned. Evidence was obtained by Moore, for example, which suggested that the defensive reaction of the host was an essential factor in the cure, optochin, in doses inadequate to kill the pneumococci, rendering them liable to the action of specific antibodies; and some experiments of Felton and Dougherty suggest that an excessive dose of an alkaloid of this class, by suppressing the natural defensive reaction, may even allow the fatal spread of an infection which a lower dose would cure. Morgenroth, on the other hand, emphasises the part played by the organotropic properties of optochin and vuzin, in enabling the red corpuscles to act as carriers of the drug to the point of action, and the connective tissues to form local depots of it.

An acridine dye, named Trypaflavin, was under study in Ehrlich's laboratory in 1914 as a trypanocidal remedy, and was found during the war, by Browning and his co-workers, to have valuable properties as an antiseptic for infected wounds and mucous membranes, for which, under the name 'Acriflavine,' it is still used. Since the war, other dyes of this series have been investigated by Morgenroth and his school, and one of them, called Rivanol,' is stated to be particularly effective as a tissue antiseptic, especially in conditions of spreading infection due to streptococci.

NH2

C2HO

NH2

N

'Rivanol' (2-ethoxy 6, 9 diamino acridine).

In the case of Rivanol' also, evidence has been brought forward that it is fixed by the red corpuscles and the subcutaneous tissues, protected thereby from excretion, or held at the point where its curative action is required. From these body cells it is suggested that the dye is gradually given up to the cocci, on which its action is exerted, by a process called transgression' by Morgenroth. This is a process by which a substance is passed from one medium to another, when both have strong affinities for it, through a layer of an intervening medium for which it has no affinity, and in which it may be almost insoluble. In this process of depot formation, and gradual liberation of the active substance, we are concerned with a phenomenon which certainly has a widespread importance for chemotherapeutic action. We have earlier seen evidence of such fixation and gradual release in the cases of Bayer ́ 205 ' and Salvarsan.

Another suggestive feature of the action of 'Rivanol' on streptococcal infections, is that such organisms as escape the immediately lethal effect of the dye appear to have lost their hæmolytic properties, and to have been modified into a relatively avirulant strain.

VII. Conclusion.

We have considered but a few examples of the directions in which chemotherapeutic investigation has proved practically fruitful, including some in which it shows, at the moment, the most hopeful signs of progress. If one considers any one group of investigations by itself, one may easily feel, at the same time, elated by the practical success obtained, in the cure of some infection which, but a few years ago, seemed beyond the reach of treatment, and depressed by the disharmony between the results of experiment and the theoretical conceptions, hitherto available, of the nature of the chemotherapeutic process. Some of the most notable practical triumphs in this field have resulted, not from experimental investigations based on theory, but from an almost empirical trial, on human patients suffering from one type of infection, of a remedy which had experimentally shown promising results in infections of a different, and sometimes of a widely different, type. The partial success of tartar emetic in trypanosome infections might have justified a hope that it would have some effect in kala-azar, but hardly a prediction of its really remarkable efficacy in that previously intractable form of infection. Still less would it have justified expectation of the brillant success of this same drug in infections by the Schistosoma or Bilharzia-worm, which but recently seemed almost beyond the hope of any kind of treatment. With such instances in mind, one might, but a year or two ago, have been tempted to suggest that the attempts at theoretical investigation, of the intimate mechanism of the chemotherapeutic process, had contributed little to the practical achievements, and that a reasonably intelligent empiricism was still the safest guide. I do not think that the suggestion would even then have been defensible, and it would assuredly have been stultified by the results of the past few years. Patient, systematic exploration, by routes of which the initial sections were already mapped in the early days of chemotherapy, has in these recent years again led to results of major importance, both for practical therapeutics and for the theoretical basis of future advance. That the original theoretical framework begins to show itself inadequate for the expanding fabric is good reason for its reconstruction; but we may well beware of hasty and wholesale rejection, remembering that it served the early builders well. I think that it is especially encouraging to note that, though, in the action of almost every remedy which has proved its value in the specific cure of infection, there are features which cannot be interpreted by a strict application of Ehrlich's distribution hypothesis, the discrepancies begin to show a new congruity among themselves. Repeatedly we find phenomena which point to the need of modifying the theoretical structure in the same direction. The conception of a remedy not killing the parasites immediately, but modifying their virulence, or lowering their resistance to the body's natural defences; of a remedy not acting as such, but in virtue of the formation from it in the body of some directly toxic product, either by a modification of its structure or by its union with some tissue constituent; of an affinity of the remedy for certain cells of the host's body, leading to the formation of a depot from which, in long persistent, never dangerous concentration, the curative substance is slowly released; all these conceptions present themselves, again and again, as necessary for our

present rationalisation of the effects observed. It can hardly be doubted that they will potently influence the methods by which, in the immediate future, new and still better specific remedies are sought. But though our practical aim, in relation to the affinities of a remedy for the parasite and for the host's tissues, may be radically changed, the meaning of these specific affinities, so delicately adjusted to a precise molecular pattern, remains dark. Ehrlich's chemoreceptors may no longer satisfy us, but we have nothing equally definite to replace them. I have endeavoured to indicate what seem to me hopeful signs of new contacts between biochemistry and chemotherapy. There is promise, in another direction, that at least some aspects of the problem of immune specificity are being brought within the scope of strictly chemical investigation, as in the recent work of Avery and Heidelberger, on the constituent of a pneumococcus which combines with the specific precipitin. As in Ehrlich's pioneer work in chemotherapy, it can hardly be doubted that an increased understanding of the meaning of immune specificity, which but a short while ago might have seemed hopelessly beyond the range of attack by chemical weapons, will still influence ideas, and help to shape the course of further investigations, on the chemotherapeutic process. As the biological complexity of the problem is realised, it becomes increasingly a matter for wonder and admiration that so much of practical value has already been achieved -the treatment of the spirochaetal infections, syphilis, yaws and relapsing fever, revolutionised; Leishmania infections, kala-azar and Baghdad boil, and Bilharzia infections, which crippled the health of whole populations in countries such as Egypt, now made definitely curable; trypanosome infections, such as the deadly African sleeping-sickness, after years of alternating promise and disappointment, brought now at last within the range of effective treatment. And if such results have already been attained, in a period during which practice has often and inevitably outrun theory, we may well be hopeful for a future in which fuller understanding should make for more orderly progress.

SECTION J.—PSYCHOLOGY.

PURPOSIVE STRIVING AS A FUNDAMENTAL CATEGORY OF

PSYCHOLOGY.

ADDRESS BY

PROFESSOR WILLIAM MCDOUGALL, F.R.S.,

PRESIDENT OF THE SECTION.

WE who are workers in the various fields of Psychology are happy in the knowledge that our science is rapidly developing, extending its influence into every sphere of human activity. The institution and the success of this Section of the British Association are good evidence that our colleagues in the other branches of natural science have recognised the claim of Psychology to take its place among those other branches. And, though in Great Britain there are still all too few Chairs of Psychology, in Canada and America the Universities and Colleges are now providing abundant opportunities for teachers, students, and research workers, opportunities that are being eagerly and fully used.

Yet, in spite of this happy state of affairs, there is manifested among us psychologists a certain uneasiness as to the status of our science, an anxiety lest the psychologist be regarded as not quite really and truly a man of science. This anxiety is, I think, exerting an unfortunate influence on the development of our science, an influence which shows itself in two principal directions.

On the one hand is a group of psychologists who, actuated by the desire to mark off an exclusive field of study as their province, define psychology as the science of consciousness and would confine themselves to the analytic description of conscious states as complex conjunctions of elements or units of some kind. On the other hand are those who, feeling that such analytic description, whether it resolves consciousness into a complex of sensations or atoms of consciousness, or into larger more complex units (the so-called configurations or Gestalten), brings but little light on human nature and conduct, and can hardly claim to be in itself a science, are driven to the opposite extreme; they ignore this realm of facts, alleged to be the peculiar and distinctive field of psychology, and they would bring to the study of man only those methods of observation, description, and explanation which are used in the physical sciences. These two tendencies, which, when they are carried to extremes, result respectively in what is unfortunately called 'structural psychology' and in behaviorism,' although so different in their outcome, are but two expressions of one desire, the desire to make psychology conform to some preconceived notion of what a science is or should be. The structuralist '