natural selection; as the fittest to survive under certain conditions is often not the best ethically but the worst. "In one aspect," said a leading naturalist, Sir William Thiselton-Dyer, "the religious sentiment is a response to a craving for a supernatural sanction to rules of conduct. Its varied but practically universal manifestation amongst mankind has to be accounted for by evolution just as much as the possession of a vertebral column. It is not practically helpful to dismiss it as irrational.”

No philosophic biologist would now insist that the principle of natural selection, or any other plan of organic evolution which leads up to man, is a complete expression of the origin and expansion of human consciousness; but most naturalists are satisfied that the principle truly represents perceptual operations of Nature. Beyond this concept there may be a new and transcendental philosophy, but it belongs to the realm of metaphysics rather than to that of observational science.

CHAPTER VIII

CONQUEST OF DISEASE

Nowadays the serpent that bites man's heel is in nine cases out of ten microscopic. Prof. J. A. Thomson.

Every disease has its own particular mode of production from natural causes. Hippocrates.

Like other natural laws, the laws of health are inexorable Ignorance of the laws is not admitted as an excuse any more than motive; and the sentence for breaches is true now as it was ages ago: "The soul that sinneth it shall die." Sir Lauder Brunton.

Just as the mechanical sciences, when viewed from a broad standpoint, represent man's struggles for the control of the energies available in his environment, so the medical sciences have, as their ultimate aim, the acquisition of control over the functions of man's body. Prof. E. H. Starling.

THOSE who transgress the laws of man sometimes escape punishment; but the laws of Nature can never be broken without paying the penalty. The man who steps over the side of a cliff, consciously or unconsciously, meets the consequences of his action swiftly, whether he be sinner or saint; and the laws of health can no more be broken with impunity than can the law of gravitation. When effects follow quickly upon causes, we learn the relationship between them readily, and from our childhood avoid actions which produce pain, as a burnt child dreads the fire. Science has shown

that a disease is just as definitely due to a particular cause, preventible or otherwise, though it may not tread closely upon the heels of action. Ignorance of the law may sometimes be pleaded in a court of justice in palliation of an offence; but Nature accepts no such excuses and decrees a punishment for every crime against her. She never forgives a fault or extenuates it; inexorable is her judgment, and inevitable her sentence, which has often to be suffered not only by the offender but also by his children, even to the second and third generations.

66

This is a hard saying; yet it is true, and there is no escape from what it implies. As we have to subscribe to Nature's statutes, it is desirable that our knowledge of them should be as complete as possible. Give me understanding and I shall keep thy law; yea, I shall observe it with my whole heart." Where such understanding does not exist, disease is regarded either as a demon to be exorcised or an "act of God" for which penitence and prayer are remedies. Ignorance made plague the terror of Europe in the Middle Ages; science has proved that the disease is due to a bacillus which is conveyed by fleas from rat to rat, and from rats suffering from the disease to mankind. Ignorance ascribed malaria to a miasma or bad air arising from marshy places; science has shown it to be caused by a micro-organism carried from one man to another by a certain species of mosquito. Ignorance of the cause of yellow fever made the regions around the Caribbean Sea the White Man's Grave, where the risk of death for the visitor was greater than in a battle; knowledge that the disease is associated with a parasite which is communicated from an infected to a healthy person by the bite of a particular mosquito, has been the

means of converting the same places into tropical health resorts.

When nothing is known of the natural laws of a disease mankind is helpless against it; but when science has discovered the enemy a sound basis can be secured for a plan of campaign to exterminate it. Plague has to be fought by the destruction of rats where it prevails, as well as by better housing and sanitation; malaria and yellow fever have to be kept under control by the continual clearance of breeding-places of mosquitoes in infected areas. Administrative measures based upon the teaching of science have practically abolished plague from the cities of Europe, have cleared Havana, the Isthmus of Panama, the West Indies, and Rio de Janeiro of yellow fever, and have made the Roman Campagna almost free from malaria, though formerly few men. who went to the district could hope for more than three years of life in it.

Practical acquaintance with ailments may be obtained by watching the sick and administering drugs, but this clinical experience is not of much use in determining the nature and origin of disease. For centuries, physicians have made their comforting presence felt at the bedside of their patients, but their observations have contributed little to the knowledge of the causes of diseases, the means of conferring immunity, or of providing antitoxins or chemical antidotes which by their specific action upon the virus of diseases successfully save human beings, as well as the lower animals, from death and incapacitating illness.

In the struggle against diseases and the discovery of means of stamping them out and preventing their development, we must not look for help to the popular physician, but to the bacteriological or the chemical

laboratory where scientific research is being carried on, often under harassing conditions and always with inadequate recompense. The ordinary medical practitioner, like the engineer, makes use of scientific results for the benefit of mankind, but originates little for himself. He is able and practical, good at diagnosis and clever in manipulation, but withal an empiric, wanting in scientific ideals and only very occasionally a contributor to scientific knowledge.

Every year an immense amount of time, labour and money is consumed in dealing with the effects of the various diseases to which humanity is liable, and in attempts, more or less successful, to cure these effects, while comparatively little is done toward preventing them by the removal of their chief sources or primary causes. The few brilliant examples which show such striking success in the latter direction only serve to throw into more prominent relief the magnitude of that deplorable amount of loss-in life, health and wealthwhich is still waiting to be dealt with.

It is a truism well recognised by medical men that the soldier has much more to fear from the ravages of disease than from the fire of the enemy. During the South African war, the British Army lost nearly twice as many men from preventible diseases, chiefly typhoid fever, as it did from wounds received in battle. In the Spanish-American war, there were twenty thousand men, or one-sixth of the American force, laid by with typhoid. On the other hand, scientific investigation into the cause of beri-beri-which had impaired the efficiency of the Japanese fleet by almost 50 per cent. during previous years resulted in the complete abolition of this disease from the Japanese ships from 1886 to 1893, and not a single case developed during the war with Russia, amidst