and group psychology since social traditions and class consciousness as well as personal passion are concerned, which helps to explain the lack of response to the appeals of the enthusiastic eugenist.

That reduction in fertility has been of long standing is strikingly illustrated by Crum's 47 study of the New England genealogies, in which he finds a progressive reduction in the size of the family and an increase in the proportion of childless marriages.

The decline among the professional classes in Britain, even when variations in age and length of marriage are allowed for, is a marked feature of the census of 1911. Of the other classes, miners, agricultural and other labourers have families above the average size, artisans are about the general average, while textile workers and other factory operatives have smaller families. The divergence between the different social classes was less marked in 1850 and reached a maximum in the nineties.

The differential death rate, chiefly due to infant mortality, to some extent modifies the initial differences in fertility; while the high fertility of the agriculturist is largely opposed by the low marriage rate and the relative infertility of the upper classes is exaggerated from the same cause. Both total and effective fertility are affected by female occupation, which tends to restrict the number of births, and also to increase the infant mortality owing to the absence of maternal care for a large part of the day. Such occupations are most common in the case of wives of textile operatives, themselves accustomed to factory and mill life from a relatively early age, and among the wives of the labourers in the towns.

The influence of differences in effective fertility in changing the distribution of the population among different social classes can be seen from a comparison of two tables, the first of which gives the percentage of each social class among the married couples, and the second the percentage of these classes among the surviving children from such parents.48

47 Crum, Quarterly Journal, American Statistical Association, 1914.

48 Census of England and Wales, 1911.

This means, to take a concrete example, that the miners who form only 8.7 per cent. of the parent class provide 10-7 per cent. of the surviving children. The unskilled labourers, the mining and the agricultural classes thus appear to be gaining at the expense of the upper and middle and the distributing classes. Miners and agriculturists are usually of good physique, though from the mental standpoint the change is possibly dysgenic.

There appears to be a general impression that the number of defective individuals, particularly of those suffering from mental defect, is greatly increasing. There is little evidence on this point of a comparable nature, but it may be definitely said that in London no such increase has taken place during the last fifteen years. The stocks from which defective individuals come are certainly often prolific, but the infant mortality is high. Indeed, so far as those individuals who are themselves mentally defective are concerned, the figures from institutions indicate death rates from ten to twenty times as great as those of the normal population. The figures regarding the defectives who have been kept under supervision in their own homes indicate rates far above the normal, though perhaps less than those in the institutions to which the worst cases naturally drift. Contrary also to popular belief mentally defective individuals do not mate in nearly as high a proportion as the normal. Out of some 360 defective girls who, while remaining outside an institution, have been under supervision during the past ten years and who are of reproductive age, only eighteen have married and only seventeen have had illegitimate children, a figure which, if regrettably above zero, is not one to cause alarm. Of their children a large proportion appear up to the present to be of normal capacity. There is some reason for thinking that there is a great intermarriage between defective stocks, and that the actual number of such stocks is in reality quite limited.

The London school service has collected information as to the size of the families one member of which has come to notice on account of mental deficiency. The figure will naturally appear higher than one derived from the census returns, since no knowledge exists concerning childless families of the same stocks or of families in which all the children had died. The figures are corrected to show only completed families which have been taken as those where the mother, at the time of the inquiry, had died or had attained the age of forty-five, and, for purposes of comparison, similar figures are given for the families of children who had obtained scholarships.

As the differential death rate continues to act there is reason to think that the defective stock are the less effectively fertile by the time the reproductive age is reached. If it be remembered that the factors act still more severely against those themselves actually defective, the reason why the defective has not overrun the country is evident. Experience in any

children's hospital or infant welfare centre reveals the handicap against the children of the mentally inferior parent.

There remains one important factor bearing on physique-namely, emigration. Since the early part of the seventeenth century the British Isles have sent abroad large numbers of the most efficient of their people, agriculturists and skilled workers of all kinds possessed of just the qualities which the nation demands for its own physical good. Where these have come from somewhat isolated areas the result has been a steady loss of the best, with the consequent replacement in the next generation by the offspring of an undue proportion of the next best. This clearly has a dysgenic effect, and it is often stated that this is the cause of the inferior calibre of the inhabitants of some remote hamlets. This-probably the most serious drain to which the nation has been, and still is, exposed— can only be regarded with equanimity on the ground that England's loss is the gain of the daughter nations. The emigrants have been largely of Nordic' and Prospector' stocks, seeking a wider scope for their energies, and the result will in the end seriously modify the racial composition of some parts of the British Isles, particularly Scotland. So far as there has been any difference between rural and urban areas it is distinctly the former that have supplied the higher proportion of emigrants. Emigration, indeed, in recent years has been a serious factor in rural depopulation.

Summarising the whole survey I would submit that a pessimistic view of the physical or mental condition of the people of England is unnecessary and unfounded. Stature and weight at least are not less than in the days of the Making of England,' of Agincourt or of Waterloo. The great war showed the possession of powers of resistance to physical adversity that have never been equalled, and under a test applied to a proportion of the nation never before approached, while the versatility of inventive powers was demonstrated everywhere. So far as the children are concerned, education is more general and the ladder wider and more used than at any period in our history. The general health of the nation is better and the expectation of life longer than ever before. There are no grounds for thinking the physical conditions of any class are worse than that of corresponding classes at previous epochs, even among those persons and classes on whom the adverse conditions of life associated with urbanisation and industrialism have pressed hardest and have been least opposed. The real increase of the unfit is much less than has been assumed from a priori arguments. Reproductive selection which has a tendency to increase the apparently less valuable stocks is opposed by a lethal selection which has not been abolished, while emigration from the eugenic standpoint, though a real disadvantage to England, has been a source of strength to the Empire of Associated Nations. The dysgenic tendencies of industrialism are being successfully opposed by the higher level of general culture and the awakening of a national conscience, but more especially by the more intelligent care for the children of the nation, in which the application of preventive medicine to education is playing no mean part. The Education Acts, if they have not revealed every child as a potential university scholar, have proved the best of Public Health measures; while all available evidence points to the intellectual average being equal to that of any other country. Civilisation may be making greater demands

1924

Р

on its bearers, but their qualities are neither diminishing nor deteriorating and more and more are fitted to shoulder the burden.

A younger country in developing its industries can profit by the experience of the older and secure from the start better hygiene and a more effective education, can watch over its most favourable racial elements, establish a public opinion favourable to the early segregation of degenerate types, and, as Canada is doing, can limit immigration to those fit to become citizens of the great Dominion.

Periodical surveys are necessary to check the changes in the population. Failing more extensive measures these may be effected through the records of the medical inspection of school children, though in these anthropometric data are but scanty. Toronto has long been known for its standard survey, and it is to be hoped that similar data will be collected in all parts of the Dominion. The matter is of great importance, since it is only on the basis of careful physical and mental surveys that legislation directed towards social and racial hygiene could properly be introduced and rightly justified. The lack of such information has been a great handicap to the discussion of such measures in Britain, and has allowed a freer play to pessimistic views.

None the less, despite all forebodings, it may confidently be stated that the Mother Nation has remained true to herself and deserves now, as of yore, the encomiums of the 'Polychronicon': 'Engelond ful of pley, fremen well worthy to pley, fre men, fre tonges, hert fre, fre helth al the leden.'

49 R. Higden, Polychronicon, Trevisa's trans., vol. ii., p. 19.

SECTION I.-PHYSIOLOGY.

PROGRESS AND PROSPECTS IN
CHEMOTHERAPY.

ADDRESS BY

H. H. DALE, C.B.E., M.D., F.R.S.,

PRESIDENT OF THE SECTION.

Introductory.

In the mind of every physiologist visiting Toronto to-day one recent advance in our science will certainly be uppermost. We rejoice with our colleagues here in a great achievement which has opened new vistas of knowledge to exploration, has brought relief to unmeasured misery, and has turned the eyes of a world, too often careless of such things, in proper gratitude and well-founded hope to this University and its Medical School. Insulin, and its still marvellous and mysterious action, have held a prominent place in the interest of many of us, myself included, during the past year or two. In one of our meetings, however, we shall have the opportunity of considering the observations and opinions of many who are now working on its properties and their significance, and among them will be some who were associated with its discovery. I have thought it appropriate, therefore, to ask your attention to-day to some recent developments in a widely different field of investigation. The subject which I have chosen presents points of general physiological and biochemical interest, apart from its immediately practical importance for the treatment of disease. It has, further, in one way, a special appropriateness to this year's meeting of the British Association. For our knowledge of an important group of diseases, caused by the parasitic trypanosomes, which have provided the experimental material for a very large proportion of chemotherapeutic investigations, we are in the largest measure indebted to the pioneer work of the distinguished President of the Association, Sir David Bruce.

I. The Theoretical Origin of Chemotherapy.

Chemotherapy may be defined as the specific treatment of infections by artificial remedies. The object of those who study it is to find new remedies which will cure or arrest diseases due to infections, not by alleviating the symptoms or invigorating the patient, but by directly and specifically suppressing the infection. Chemotherapy, in this wide sense, is not entirely of recent growth. When the natives of Peru discovered the value in fevers of the cinchona bark, which the Jesuits brought to Europe in the 17th century, they had found a specific remedy for malaria, which is still the best available. Similarly the natives of Brazil had found in ipecacuanha, which reached Europe shortly after cinchona, a remedy for amoebic dysentery better than any other which our modern systematic