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rate in the members of both sexes of the Royal Houses of Europe (Westergaard, p. 284).

From 1841 to 1850, in England and Wales 162'81 individuals out of every thousand of both sexes died annually, but the corresponding figure for the period 1881 to 1890 was decreased to 153'67 per thousand.

Westergaard (p. 296) has displayed in a most useful table the mortality in the chief countries of Europe and in the State of Massachusetts, in two periods of time. In the case of old persons from 70 to 75 years, there has been a constant decrease in the death-rate, without any exceptions. The exact statistics collected by Pension Bureaus and Life Assurance Companies exhibit the same general tendency.

It cannot be disputed then that there has been a general increase in the duration of life, and that old people live longer at the present time than in former ages. This fact, however, cannot be taken absolutely, and it is still possible that in particular cases there may have been more centenarians hitherto than at present.

The prolongation of life which has come to pass in recent centuries must certainly be attributed to the advance of hygiene. The general measures for the preservation of health, although they were not specially directed to old people, have had an effect of increasing their longevity. As in the 18th century and for the greater part of the 19th, the science of hygiene was in a very rudimentary condition, we may well believe that improvement in cleanliness and in the general conditions have contributed largely to the prolongation of life. It is now a long time since Liebig said that the amount of soap used could be taken as a measure of the degree of civilisation of a people. As a matter of fact, cleanliness of the body brought about in the most simple way, by washing with soap, has had

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a most important effect in lessening disease and mortality from disease. In this connection, the fact recently published by Prof. Czerny,1 a well-known German surgeon, has a special interest. Although cancer, the special scourge of old age, has increased in recent times, one form of the disease, cancer of the skin, has diminished notably. "Cancers of the skin," Prof. Czerny says, are met with almost exclusively on uncovered regions of the body, or on parts accessible to the hands. They develop especially where the susceptibility is increased by ulcers or scars which are easily soiled. And so it happens that in the classes where care is taken as to cleanliness cancer of the skin is very rare and certainly much more rare than it used to be."

M. Westergaard thinks that vaccination against smallpox has been of considerable importance in lowering the death-rate in the 19th century. This, however, can have had little effect on the duration of life in old people, as deaths due to small-pox in the old are excessively rare. For instance, in the second half of the 18th century, that is to say before the introduction of Jenner's method, the mortality from small-pox at Berlin was 98 per cent. of all the deaths, but of these only o'6 per cent. were cases of persons more than fifteen years old. The rest, that is to say, 99'3 per cent. fell on children under that age. It may be supposed that most of the old people at that time were already protected by previous attacks of small-pox, contracted when they were young.

If hygiene were able to prolong life when it was little developed, as was the case until recently, we may well believe that, with our greater knowledge of to-day, a much better result will be obtained.

1 Medizinische Klinik, 1905, No. 22.

III

DISEASES THAT SHORTEN LIFE

Measures against infectious diseases as aiding in the prolongation of life-Prevention of syphilis--Attempts to prepare serums which could strengthen the higher elements of the organism

ATTACKS of infectious diseases incurred during life frequently shorten its duration and it has been observed that most centenarians have enjoyed good health throughout their lives. Syphilis is the most important of these diseases. It is not really a cause of death itself, but it predisposes the organism to the attacks of other diseases, amongst the latter being some particularly fatal to old people, such as diseases of the heart and blood-vessels (angina pectoris and aneurism of the aorta) and some malignant tumours, especially cancer of the tongue and of the mouth. To lengthen human life, it is a fundamental necessity to avoid infection by syphilis. To reach this result everything must be done to spread medical knowledge about such diseases. It is absolutely necessary to overcome the deeply rooted prejudice in favour of concealing everything relating to sexual matters. Complete information should be widely spread as to the means of protecting humanity against this awful scourge. It has now been possible to apply experimental methods to the

investigation of this disease, and science has obtained a series of results of the highest practical utility. Prof. Neisser of Breslau, one of the most distinguished of modern venereal physicians, has summed up the present state of knowledge of these matters in the following lines.1 "It is our duty as medical men," he says, "to recommend strongly as a means of disinfection in all possible cases of contagion the calomel ointment which Metchnikoff and Roux have advised." It is to be hoped that future generations, by following this advice, will see an enormous diminution in the number of cases of syphilis.

Syphilis, however, although a very important factor, is not alone in shortening the life of man. A very large number of persons die prematurely although they have not contracted that disease. We do not know the duration of human life before the arrival of syphilis in Europe, but there is no reason to think that it was very different from what it is to-day. We must, therefore, try to prevent as many infectious diseases as possible, and recent advances in medicine have made this task much less difficult. Pneumonia, it is true, the most common infectious disease amongst the old, cannot yet be easily avoided. All the antipneumonic serums which have hitherto been prepared have turned out to have little efficacy; but there is no reason to give up the hope that this problem will yet be solved.

Diseases of the heart, which are common in extreme old age, are particularly difficult to avoid, because in most cases we do not know sufficiently well their primary causes. In so far as they depend upon intemperance or infectious diseases such as syphilis, they can be avoided by the employment of suitable measures.

As the higher elements of the body in old people become

1 Die experimentelle Syphilisforschung, Berlin, 1906, p. 82.

weaker and are devoured by the macrophags, it seems probable that the destruction or deterioration of these voracious cells would tend to the prolongation of life. However, as the macrophags are indispensable in the struggle against the microbes of infectious diseases, and particularly of chronic disease, such as tuberculosis, it is necessary to preserve them. We must turn rather to the idea of a remedy which could strengthen the higher elements and make them a less ready prey to the macrophags.

In the "Nature of Man" (Chap. III.) in discussing the simian origin of mankind, I touched on the existence of animal serums that have the power of dissolving the blood corpuscles of other species of animals. There is now, in biological science, a new chapter upon such serums, which have been called cytotoxic serums because they are able to poison the cells of organs.

The blood and blood serum of some animals act as poisons when they are introduced into an organism. Eels and snakes, even non-poisonous snakes, are cases in point. A small quantity of the blood of a snake, an adder for instance, injected into a mammal (rabbit, guinea-pig, or mouse) soon brings about death. The blood of some mammals is poisonous to other mammals, although in a lesser degree than that of snakes. The dog is specially notable from the fact that its blood is poisonous to other mammals, whilst, on the other hand, the blood and blood serum of the sheep, goat, and horse have generally little effect on other animals and on man. It is for this reason that these animals, and particularly the horse, are used in the preparation of the serums employed in medicine.

Now, these harmless serums become poisonous when they have been taken from animals which have been first

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