It is a hard saying, but none the less a true one, that the bacillus tuberculosus is a friend of the race, for it attacks no healthy man or woman, but only the feeble. It is like the bacillus of leprosy in this respect, but in this respect only, for leprosy attacks anyone living under certain unhygienic conditions. Remove these conditions—as we have done long ago—and the bacillus of leprosy disappears; its duties are over, like those of the extinct plants and fishes in the rocks.
The tubercle bacillus on the other hand attacks a type to be found not only in the poor, ill-fed, and ill-conditioned, but also those who live well. It is a disease of all classes, and those who live in well-ventilated rooms, and who conform to every sanitary regulation, may still belong to the type who fall a prey to it. It is certain, therefore, that, improve the external conditions of life how you will, this type will remain. It is also as certain that in giving the type a better chance than it has already, by preventing infection or by delaying the disease, the type will be more and more prevalent as each generation comes to life.
It comes out pretty clearly from our short study of the infective diseases that some of the microbes that cause these, such as the bacillus of tubercle, only feed on unhealthy human tissue, while the greater number of them kill, if anything, the weak rather than the strong. They are, therefore, on the whole, and as a natural consequence, our race friends rather than our foes, and if we attempt seriously to do away with their selective influence—viz., the elimination of the weak and the preservation of the strong—we must supply this selective influence by one equally potent, or the race will tend to deteriorate. What can be done in the future, and what it is expedient for us to do at the present time, will be more fully discussed in a subsequent chapter; but I may state at once that pari passu with our endeavour to prevent these diseases must be our efforts to enlist the co-operation of the human charity that would avert suffering in such selection as shall necessitate the birth of future generations from the healthiest and best of those amongst us. As selection is the race-changer, we must replace the selection of the microbe by the selection of human forethought.
A number of diseases, which are due probably to innate family predispositions, are known to us. Of these diabetes, hæmophilia, and some others are of comparative rarity, and may be left on one side in this necessarily contracted sketch. Others, such as cancer and constitutional weakness of the respiratory and other organs, as well as insanity, are frequent enough to merit our close attention. Of cancer we at present know too little, and I propose to leave it on one side. Of inherited weakness of special systems we have many examples, such as a delicate respiratory or digestive mucous membrane, inherited variations in the mechanism of assimilation, and also gout and obesity—in fact, innate delicacy of all kinds, which renders their possessor less able to cope with his natural surroundings, let these be what they may.
There is hardly a family that can boast of the complete want of hereditary weakness, and among the children of particular families, where these weaknesses exist, some show the taint more than others. In times of hardship, cold, exposure, coarse food, etc., these weaker ones perish, and the race is consequently propagated from the stronger ones. Within certain limits cold, exposure and coarse food are compatible with great physical excellence, for the cold and exposure, hurtful to the sickly, braces and hardens the more robust, and coarse but nutritive food supplies him with energy and strengthens the powers of digestion. The finest races have been bred by hardship. It is proverbial to speak of “the hardy mountaineer,” and one cannot look at a lowland Scot without feeling that his stock had, in days gone by and for many centuries, run the gauntlet of oatmeal porridge and cold east wind.
But we are rapidly diminishing those selective agencies which in the past have developed race vigour. As we shall presently see, skill in nurturing the sickly has, in modern times, wonderfully reduced the mortality amongst infants; improvements in methods of nursing, the replacement of cotton by flannel and wool, and the use of many foods, some of them artificially digested, gives a sickly infant a chance of living, and it survives its first most dangerous years. Then its chances are again improved, for the infective diseases are being held in check, and it has comparatively little to fear from them. Thus it survives and lives to adult age, when, like the hothouse plant, it is still protected from hardships to which the race had formerly been freely exposed. It lives to lower the average physique of the mothers or fathers who produce the next generation of children.
This increased preservation of the sickly has had the effect of increasing the life period of an average child, and this increase in the life probability is often and very rightly cited as an indication of the improved sanitary conditions of the people. Improved sanitary surroundings, as we have seen, are taken advantage of chiefly by the sickly, and thus with our increased probability of life we have diminished the average robustness of constitution, or innate healthiness of the race, for a larger proportion of sickly ones are living amongst us. In our day a greater number of parents suffer from phthisical, scrofulous and other taints than in days gone by, and these and other taints are passed on to their children.
So far we have seen what of necessity follows from our biological premises, but it is also possible, I think, to show by statistics that already very observable deterioration has taken place.