swing of the pendulum bringing into play a preponderating pithecanthropic element. And the pendulum would appear to swing so regularly, that, given the requisite biological data, he would even be able to forecast which would be the fat and which the lean years of a nation's future. Can anything more be expected of science than this?

The second theory of causation is that these retrogressive variations are not caused, but arise of themselves; in other words, that they are 'spontaneous' in origin. Thus, in the Report of the Royal Commission on the Feeble-minded the following statement occurs: 'Both on the ground of fact and of theory there is the highest degree of probability that feeble-mindedness is usually spontaneous in origin, that is, not due to influences acting on the parent.' Now, as Huxley remarked many years ago, to say that a variation is spontaneous is simply to express our ignorance of its causation; and it is obvious that this theory of 'spontaneous variation' is extremely unsatisfactory. The more we learn of the phenomena of nature, the more do we find evidence of law and order; and it would be strange, to say the least, if chance and not law should control what is probably the most important happening in the whole of nature.

The third view is that retrogressive germ-variations have neither existed ab initio nor are spontaneous in origin, but are produced by the operation of natural processes and in obedience to natural laws. In my opinion this is not only the most reasonable view in itself, but the only one which is supported by definite evidence; and, although it is not yet possible fully to explain the manner of production of these germ-variations, it is possible to advance certain considerations which at least possess the merit of carrying us a step further towards the elucidation of this problem.

If we pass for a moment from the germ-cells to consider the cells of the body, we find that retrogressive changes occur under two conditions: firstly, in consequence of an endogenous decline of their vitality; secondly, through the action of external agencies. The former of these changes occurs in old age. By this is not meant old age as expressed by years; some persons are old at forty, others still young at eighty. What is

meant is that condition of senescence which results from the exhaustion of the inherent vitality of the cells. They are unable to function because they have come to the end of their physiological banking account. Decay arising from without is best exemplified by the action of such inorganic and organic poisons as alcohol, lead, and phosphorus, or by toxic bodies produced by certain microorganisms. These agents may bring about such a deterioration of important cells and tissues that the death of the individual results. The problem we have to consider is whether the germ-cells may be affected by similar agencies. May they undergo pathological variation in consequence of senescence? May the same result be caused by adverse factors of the environment?

To begin with the first of these questions-as the modern conception of the continuity of the germ-plasm has become popular, it is not infrequently said that this plasm is 'immortal.' But, even if it be granted that germ-plasm existing to-day is the lineal descendant of plasm which has existed since the origin of life, this statement requires some qualification. The unexpended germ-cells not only die, of course, at the death of the individual, like any other piece of protoplasm, but they may die, or at all events lose their capacity for reproduction (which comes to the same thing), whilst the ordinary somatic cells are still alive. This commonly takes place in women between the fortieth and fiftieth year. Now, it has been noticed by several observers that children born towards the end of the female reproductive period tend to be feebler than those born whilst the generative organs are in full vigour. Possibly this, in part, may be due to a senility of the maternal tissues which nourish the seed, but it is equally likely to be due to a senility of the seed itself, so that there is some ground for thinking that senescence may be a possible cause of pathological germ variations.

Again, there are certain Infusoria, which, while ordinarily multiplying by fission, from time to time undergo a form of conjugation not unlike that which occurs between the sperm and germ-cells in human beings. It was shown by Maupas that, if this periodical conjugation is prevented, the offspring resulting from subsequent fissions gradually undergoes a form of degradation until

the whole group eventually becomes extinct. Prof. Marcus Hartog argues from this and similar researches made by other enquirers that conjugation or fertilisation plays an important part in warding off senescence. such introduction of fresh blood necessary to ward off senescence and prevent germinal impairment in the case of higher animals, human beings in particular? With regard to certain domestic animals, there is reason to think that close in-breeding is followed by a gradual deterioration of offspring; and experienced breeders are practically unanimous that the effect of this is to produce debility, abnormalities, and eventually sterility. As Sir Francis Darwin says, 'it is generally admitted that degeneration either in constitution or in other ways does ultimately ensue; so that at any cost the breeder is absolutely compelled to admit blood from another family or strain of the same race.' In the case of human beings, however, in-and-in breeding to this extent is practically unknown; and it is therefore unlikely that senescence of the germ-plasm from such a cause plays any practical part in the production of degeneracy. At the same time it is to be remarked that the effect of consanguineous marriages is to intensify any existing defect; and the same is true where mating is rigidly restricted to the members of any one small section of society. We are apt nowadays to bewail the not infrequent union of members of our old and formerly exclusive aristocracy with chorus girls and the like. The process may be attended with a serious decline in 'form' and manners; but it is possible that it may possess physiological compensations which are beneficial to the race as a whole.

We have now to consider the question of the modification of the germ-plasm by the environment. Fifty years ago few scientific persons would have doubted this; and even to-day it is probable that most medical men would say that their clinical experience supported such a view. But in those days it was supposed that the germ-cells arose, by some means or other, from the body-cells; it followed that their condition was dependent upon the condition of the body-cells, and the production of germvariations through the environment was a necessary and logical sequence. But recent writers, particularly

Professor Weismann, have proclaimed the 'continuity' of the germ-plasm; they have contended, in other words, that it is not produced anew in each individual, but is an independent plasm which is handed on from generation to generation as a separate entity; and it is consequently argued that the germ-plasm is immune to its surroundings. Some writers have even gone so far as to say not only that the environment has, in fact, no influence in the production of germ-variations, but that it cannot have any such influence, because, if it had, it would be subversive of the whole doctrine of evolution. Since this argument strikes at the very root of what I conceive to be the origin of degeneracy, it will be well to consider the basis upon which the assertion is made. And in this connexion I cannot do better than quote the words of Dr Archdall Reid, who is perhaps the most strenuous advocate of this view. Dr Reid says:

'If this theory that germinal changes may be caused by waste products, circulating toxins and the like, is correct, all races affected by any sort of disease should drift steadily towards extinction.' Again: 'If disease produces any germinal change, then, no matter how small and imperceptible the differences between one generation and the next, . . . the constant accentuation of the alteration during hundreds, perhaps thousands, of generations must make it at last manifest and unmistakable.' . . . 'The facts are decisive; nearly all human races have been exposed to disease for thousands of years, and in no instance is there to be found an iota of evidence that any race has, as a consequence, become degenerate' (pp. 260–262).

Now, at first sight these statements may appear very plausible; but a little reflexion will show them to be really fallacious in that they entirely disregard one important consideration, namely, the possibility that the vulnerability of the germ-plasm may vary greatly in different individuals. In the case of the ordinary tissues and organs of the body-the somatoplasm-there is no doubt whatever on this point; and one of the bestestablished facts in medicine is that of the varying resistance to disease presented by different individuals. Thus, one person will rapidly succumb to Tuberculosis, Influenza, Pneumonia or other toxic process; another will escape

death but evince considerable subsequent deterioration; while a third will recover without any permanent ill effects. It is surely not unjustifiable to consider that similar differences of vulnerability may exist in the case of the germ-plasm. Adverse factors of the environment will then not be operative upon the germ-plasm of the whole community, but only upon that of the susceptible portion; and it will no more follow that all races affected by any sort of disease should drift steadily towards extinction' than it follows that all persons affected with Tuberculosis, Influenza, or other disease will necessarily die of those complaints. Further, not only may some germ-plasm be practically immune, but plasm which is susceptible may be influenced to varying extent, both quantitatively and qualitatively, thereby giving rise to many different forms of variation and degrees of degeneracy.

As a matter of fact this is precisely what happens; and the manifestations of degeneracy as seen in daily life vary within very wide limits. In some instances the variation is so pronounced as to interfere seriously with the survival value of the resulting offspring. Such individuals will then be eliminated by natural selection, provided this is sufficiently rigorous, so that, far from being subversive of the doctrine of evolution, the process is one which actually conduces to racial evolution. It may happen, however, that the variation is much less pronounced and the social environment not sufficiently rigorous to bring about elimination. Such individuals will then not only be enabled to survive, but will intermarry with those whose germ-plasm is unimpaired, with the result that a dilution of the morbid process may take place so far as individual members are concerned, but there will be a more widespread dissemination throughout the community.

As will presently be shown, these milder manifestations of degeneracy occur more particularly in the central nervous system. They involve those parts of the nervous system concerned with the higher processes of mind, and they take the form of a diminished mental potentiality, a lessened vigour and initiative, a want of balance and a loss of control. The social expression of these changes is seen in an incapacity of the community