Part 4
The minute parasites which cause Malta, yellow, and malarial fever, and other infections, are no doubt best dealt with by excluding them from access to the human body when that is possible. But once they have effected a lodgment and commenced to multiply in the blood or tissues, it is still possible to get at them by means of drugs, which poison them without injuring their human victim. Thus quinine has been of enormous service in checking the ravages of the malaria parasite, and really in Great Britain has exterminated “ague,” which is the English name for malaria. Many experiments have been made during the last two years, with the view of finding some drug which will, in like manner, destroy the trypanosomes which have established themselves in the blood and lymph-passages of the human body, and are slowly killing their victim with sleeping sickness. An arsenic compound, “atoxyl,” has been found effective when injected into the patient’s body, and according to Dr. Koch, who returned last year from Uganda, he has found nothing better than this treatment, discovered by Dr. Thomas and Dr. Breinl, of the Liverpool School of Tropical Medicine, three years ago. Dr. Plimmer and Dr. Thomson, who have been experimenting in London for the Royal Society, have found a drug which is more effective than atoxyl in destroying certain trypanosomes which attack rats, and is now being tried in the treatment of sleeping sickness. This is the tartrate of sodium and antimony--a salt corresponding to the well-known tartar emetic, with this difference, that it contains sodium instead of potassium. It seems that this sodium variety of tartar emetic is very destructive to trypanosomes in the blood and lymph, and has no injurious effect of a lowering nature, such as occurs when the potassium salt is used. As the antimony drug is far cheaper than atoxyl, it will be possible to apply it freely to horses and cattle suffering from “nagana” and “surra,” which are diseases due to trypanosomes of a special kind. Two white men who had become infected by the trypanosome of sleeping sickness in West Africa have been treated with the new drug in London, and the parasites have completely disappeared from their blood in consequence, though it remains to be seen whether a permanent cure has been effected. One cannot imagine a situation of more thrilling interest than that existing in the nursing home where those two victims were given a strong hope of escape from what seemed to be certain death, whilst the fate of thousands of African natives, similarly infected, was hanging in the balance! After six months from the date of treatment the report is satisfactory. The parasites have not yet re-appeared (July, 1908) in the two patients treated in November.
14. _Tsetse-Flies and Disease_
Dr. Koch appears to have been questioned on his return to Europe by some journalists as to the results of his study of sleeping sickness during the past year and a half in Uganda. It was already known (three years ago), from the observations of Professor Minchin, Dr. Gray, and Dr. Tulloch (the Royal Society’s observers in Uganda), that the tsetse-fly in Uganda sucks the blood of crocodiles, also of fishes and of hippopotami. Dr. Koch confirms this observation. Minchin also observed a trypanosome in the blood of the crocodile differing from that of sleeping sickness. Whether crocodiles help, in an important degree, to keep tsetse-flies alive in the regions where they occur, by offering them a ready meal of blood, is uncertain. So far as the facts are known, they do not lead to the belief that the crocodile is a “reservoir host” for the trypanosome of sleeping sickness.
“Reservoir-host” is a very useful and expressive name for animals which can tolerate or support a parasite in their blood which is deadly to other animals. The parasite flourishes in abundance in the reservoir-host with entire satisfaction to both host and guest. But a blood-sucking fly or gnat, of promiscuous tastes in the matter of blood, comes along, sucks the reservoir-host a bit, and then goes off for another meal to a susceptible animal, into which it introduces the parasite now adhering to its already blood-smeared proboscis or beak. Such a history was first established by Bruce in regard to the trypanosome parasite which causes the deadly nagana disease in the “fly-belts” of South Africa. The big game animals are reservoir-hosts to this parasite, from which they are carried by the tsetse-fly to horses, mules, and dogs, which, being of foreign origin, are not tolerant of it, but are killed by the poison to which its multiplication in their blood gives rise. Thus, too, native children, both in Africa and the East Indies, appear to be tolerant of the malaria parasite, and act as reservoir-hosts from which the spot-winged gnats suck and distribute the parasite to the non-tolerant, susceptible adult natives and white men.
The tsetse-flies are little bigger than the common house-fly, and bite, or rather stab, very rapidly after alighting on the skin. The study of flies and gnats, and other blood-sucking insects, has become extremely important, and has been carried on with great energy by many specialists since it became known that these insects play such a terribly important part in the causation of disease. At the Natural History Museum I received (in response to a circular issued at my request by H.M. Government) thousands of specimens of gnats (mosquitoes) from all parts of the world, and some hundreds of new species have been described in a series of volumes by Professor F. V. Theobald, published by the trustees. Other volumes are in preparation illustrating the blood-sucking flies of various regions of the world, and one concerning those of the British Islands has already appeared. The common gnat, the spot-winged gnat, and the tsetse-fly--as well as the microscopic parasites causing malaria and sleeping sickness--are illustrated by greatly enlarged models--very carefully executed under my direction, which are exhibited in the central hall of the museum.
It is a curious fact that the coloured races of men--especially those of Africa--have little or no objection to being bitten by flies. They seem to accept the attention of flies and ticks with indifference. The men sleep in the day under trees, and are willing food-supply to the insects. The eyelids of children are literally inhabited by flies in some countries, and the folds of the skin of fat adults hide whole rows of fast-holding ticks. But the white man does not willingly permit either fly, flea, or gnat to settle on him. He is (or has been), nevertheless, unwisely tolerant of house-flies in his habitations, and the poorer and less cleanly population are in large proportion infested with wingless insects. The newly established knowledge that certain flies (glossina or tsetse-fly) are the carriers of sleeping sickness, that gnats are the carriers of malaria and of yellow fever, that fleas are the carriers of the plague, and that certain kinds of ticks are the carriers of cattle-fevers and dog-fevers, and probably of some obscure fevers of man, must make us all more anxious than we were about contact with insect life. For ages popular tradition has ascribed diseases of one kind and another in various parts of the world to the bites of flies. But actually it is little more than fifty years ago since it was really shown that deadly germs or parasites existed which could be, and actually are, carried by flies from one animal to another, and introduced into the blood by the flies’ stab. This was first shown in regard to the bacterium of splenic fever (or anthrax, or wool-sorters’ disease), a blood-disease of cattle which is transferred by the big, fiercely-biting “horse-flies” (tabanus), from animals to man, and is invariably fatal. Another bacterial disease, “pernicious œdema,” is inflicted on man in the same way. These cases were exceptional, and it is only quite recently that the agency of flies and fleas in great epidemics, and in diseases causing thousands of deaths every year in well-known regions, has been discovered.
15. _Monkeys and Fleas_
The wingless parasites known as pediculi are not known as active agents in spreading disease germs, probably because they do not readily transfer themselves from one animal to another. It is in this connection a really remarkable fact that monkeys are not infested by fleas, and that only in few cases and not in many kinds have pediculi or acari been observed. In this respect the lower races of men (and even the higher) seem to have fallen away from a grade of excellence attained by their despised quadrumanous cousins. When this fact as to the freedom of monkeys from insect parasites is mentioned, those who have watched monkeys in captivity will immediately say, “Surely I have seen monkeys carefully picking insects from one another’s fur.” The fact is that it is this very habit of “picking” which prevents monkeys from harbouring fleas. Whereas a dog or a cat can only scratch, the monkey has an opposible thumb and delicately sensitive fingers. That which has become the hand of man, with all its marvellous skill and efficiency, has been elaborated in its early stages as a means for keeping the hair clean. When monkeys are seen carefully removing something with finger and thumb from their own or their companion’s hair, it is not an insect but a little piece of fatty secretion and scurf which is thus removed. The habit, which seems to be general in all kinds of monkeys, even with the anthropoids, such as the chimpanzee and the orang, has of course been efficient in removing any parasitic insects which may at one time have infested monkeys--all other furry animals are liberally supplied with them, as also are birds--but is now preventive of any re-establishment of such visitors. The popular judgment of the monkey’s habit is similar to that of the Japanese Aino, who remarked to a traveller who arranged to have a bath in his room every day that he must be a very dirty man to require it.
16. _The Jigger Flea_
One flea is recorded as having been once taken on an anthropoid ape (a gorilla), and is the “jigger,” Pulex penetrans. This is a very serious pest, the history of which shows how man himself opens up the path by which dangerous diseases spread. The jigger-flea was originally known only in the South American tropics. It spread from there to the West Indies in the last century. It burrows into the skin, usually between the toes, but elsewhere also, and causes an abscess and sore as big and deep as a hazel-nut. Several such cavities at a time are dangerous, and often lead to blood-poisoning and death. Europeans avoid the burrowing of the jigger by having their toes carefully examined every morning, but black men are less careful. From the West Indies, about thirty years ago, the jigger was carried in ships to West Africa. There it flourished and spread from village to village across Central Africa, decimating the population. It appears to have been carried to a large extent by dogs, in whose skin it flourishes. It has now passed through Africa to India, and we shall no doubt soon hear of its having completed the circuit of the globe.
A great many kinds of fleas are known, many furry animals having their own special species, which does not leave them to take up its dwelling on other kinds of animal. The common rat has a large flea of its own, which apparently is not the flea which carries the plague from rats to men. It is a “wandering” flea which does this, namely, the Cheops flea. This flea, common in the East but unknown in colder regions, does not stay as one could wish it to do--on the rat; but travels about visiting human beings and dogs, and so carries the plague bacillus from rats to men. In the absence of these fleas plague would be a rat-disease unknown in men. It is probable that we do not nowadays live so thoroughly cheek-by-jowl with rats in Western Europe as formerly, so that even if rats infected with plague and harbouring the Eastern Cheops flea arrive in our docks, the wandering flea is too far off to reach us in our modern houses.
17. _Public Estimate of the Value of Science_
The Royal Society, the full title of which is The Royal Society of London for the Promotion of Natural Knowledge, has its anniversary meeting and dinner on St. Andrew’s Day. The health of the medallists of the year 1907 was given from the chair by Lord Rayleigh, and they replied one by one to the toast. Professor Michelsen, of Chicago, received what is considered the greatest honour the society has to bestow--the Copley Medal (founded more than two hundred years ago) for his researches on light. He related in his speech how he had tried to interest a wealthy business man in the experiments going on in his laboratory, in the hope that his friend might be moved to give pecuniary aid for the provision of new apparatus. One by one, he showed his delicate instruments and explained their uses; no impression was produced. At last he explained how the bright lines of the spectrum of flame, coloured by incandescent elements (such as theatre-goers know as red fire, green fire, blue fire, &c.), can be recognised by means of the spectroscope in the light of the sun--proving the presence of the metals and other elements of this earth in that remote body. He especially explained and showed his friend the experiments by which sodium, the metal of which caustic soda is the “rust,” is thus proved to be present in the sun. At last his friend spoke. He said: “Who the ---- cares if there is sodium in the sun?” Professor Michelsen did not tell the fellows of the Royal Society how he replied to that abrupt inquiry.
A more encouraging speech was that of Lord Fitzmaurice, the Under-Secretary of State for Foreign Affairs, who replied to the toast of the guests. He declared, in so many words, “It is every day becoming more and more certain that science is the master.” He said that in his own business as a diplomatist he found that the chief matters which he had to discuss and decide depended on scientific knowledge and the information and guidance given to him and his colleagues by scientific men. In the beginning of the eighteenth century the British Government had sent a bishop and a poet to negotiate the Treaty of Utrecht. But neither would be of any use in modern diplomacy. What they always had to seek at the present day was the aid of the scientific departments of the Navy or the Army, or of the Royal Society. Such matters as the relative merits of a Channel tunnel or a Channel ferry, the limitations of territory by land, by sea, or above the land in the air, the international agreements as to measures for checking the spread of disease or of insect pests, and, indeed, most matters which had come before him since he had been in office, had to be decided by the scientific experts. He did not propose that diplomatists should at once vacate their posts and endeavour to secure the occupation of them by men of science, but he thought that at no distant date such a course would be considered not only reasonable, but necessary!
18. _The Common House-fly and Others_
The common house-fly is not so innocent as he looks, but really a dirty little thing. He has not a sharp beak-like proboscis, and cannot stab, but he has a soft, dabbing proboscis, which he pushes on to every kind of filth as well as walking with his six legs on such matter. Then he comes and wipes off minute particles and germs on to our food, our lips, our fingers, and faces. It is quite certain that he, and others allied to him, are thus the means of spreading typhoid fever in camps where there are open latrines and open larders and mess tables. The house-fly breeds from a maggot, just as the blue-bottle or blow-fly does, but very few people have ever seen or recognised the maggot of the house-fly. The reason is that it lays its eggs in horse dung, and the grubs are hatched in the muck-heaps of stables. That is also the reason why it is much less numerous in London than it used to be, since stables and mews are now fewer and cleaner than they were. It is also the reason why the house-fly abounds in ill-kept country inns and farmhouses. Its breeding ground is just outside the window.
There is not only one common house-fly in this country: there are three kinds, in addition to the blue-bottle or blow-fly, which is distinguished at once by its great size and blue colour, and lays its eggs in carrion. Late in the year you may often see what would pass for young or starveling house-flies going about among the others. This is a distinct species, the Homalomyia canicularis of entomologists. The third kind only to be distinguished by careful examination with the aid of a magnifying glass, is Anthomyia radicum. Both these are much less abundant than the common house-fly (Musca domestica), with which they almost always occur. Their breeding habits are similar to those of the common house-fly.
A fourth kind of fly is invariably mistaken for the common house-fly when it is noticed, as it sometimes is, in consequence of the sharp stab which it inflicts. As recently as the beginning of November last year I was “bitten” or pricked by one of this fourth kind in a London club. They are common enough on the sea shore in autumn, and may be a severe nuisance. People generally take them for common house-flies which have lost their temper in the hot weather and give way to the bad habit of “biting” out of sheer exasperation. Really, of course, a house-fly could not stab or prick with its broad-ended proboscis. The fly in question, which looks almost exactly like a well-grown house-fly, but possesses a sharp and business-like beak or proboscis, is known to scientific men as Stomoxys calcitrans. There are many kinds of Stomoxys scattered all over the world, and it is probable, though not actually proved, that they carry parasites such as the trypanosomes of horse and cattle diseases from one animal to another, as do the species of Glossina or tsetse-fly.
But we have yet to learn more about these flies and the parasites they transfer. In the case of the gnat, it has been discovered that the malaria parasite is swallowed by the gnat, and multiplies in it, producing thousands of spores in its blood, and it is these spores which the gnat hands or rather “mouths” on to man. No such multiplication of the trypanosome in the tsetse-fly (Glossina) is known. The tsetse-fly passes on the trypanosome as it received it, and yet it seems as though it is not any and every biting fly which can pass on the trypanosome of nagana, or of sleeping sickness, but only the particular species of tsetse-fly. Perhaps it is a case of greater abundance, the tsetse-flies being the obvious and dangerous carriers of trypanosome disease where they occur, on account of their abundance and the fierceness and celerity of their attack. It is almost certain that in India, Burma, and South America some other flies must transfer the trypanosomes from animal to animal, causing the diseases known as surra and mal de caderas, because no tsetse-flies--that is to say, no flies of the genus Glossina--occur in those countries, and no other mode of transference, except by some blood-sucking insect, seems probable.
Ants in Africa are carriers of infection, and possibly also in London kitchens, where a little red ant sometimes abounds. The black beetle or cockroach is a creature to be got rid of, as it is very probable that it spreads certain kinds of infection over food and dishes during the hours of “revelry by night” which kind-hearted people allow it to enjoy in their kitchens.
19. _Cerebral Inhibition_
The best golf-player does not think, as he plays his stroke, of the hundred-and-one muscular contractions which, accurately co-ordinated, result in his making a fine drive or a perfect approach; nor does the pianist examine the order of movement of his fingers. His “sub-liminal self,” his “unconscious cerebration,” attends to these details without his conscious intervention, and all the better for the absence of what the nerve-physiologists call “cerebral inhibition”--that is to say, the delay or arrest due to the sending round of the message or order to the muscles by way of the higher brain-centres, instead of letting it go directly from a lower centre without the intervention of the seats of attention and consciousness. The sneezing caused in most people by a pinch of ordinary snuff can be rendered impossible by “cerebral inhibition,” set up by a wager with the snuff-taking victim that he will fail to sneeze in three minutes, however much snuff he may take. His attention to the mechanism of the anticipated sneeze, and his desire for it, inhibit the whole apparatus. So long as you can make him anxious to sneeze and fix his attention on the effort to do so, by a judicious exhortation at intervals, he will not succeed in sneezing. When the three minutes are up, and you both have ceased to be interested in the matter, he will probably sneeze unexpectedly and sharply. I was set on to this train of thought by a recent visit to an exhibition of photographs.
There were many very interesting illustrations of the application of photography to scientific investigation. Among others I saw a fine enlarged photograph of the common millipede (Julus terrestris), and my desire was renewed to have a bioscopic film-series of the movements of this creature’s legs. Some years ago I attempted to analyse, and published an account of, the regular rhythmic movement of the legs of millipedes. I found that the “phases” of forward and backward swing are presented in groups of twelve pairs of legs, each pair of legs being in the same phase of movement as the twelfth pair beyond it. But instantaneous photography would give complete certainty about the movement in this case, and in the case of the even more beautiful “rippling” movement of the legs of some of the marine worms. Some kindly photographer might take up the investigation and prepare a series of films. The problem is raised and the effects of “cerebral inhibition” described in a little poem which I am told we owe to the author of “Lorna Doone.” As it is not widely known, I give it here as a record of “cerebral inhibition”:
“A centipede was happy ’til One day a toad in fun Said, ‘Pray which leg moves after which?’ This raised her doubts to such a pitch She fell exhausted in the ditch, Not knowing how to run.”
The point, of course, is that she could execute the complex movement of her legs well enough until her brain was set to work and her conscious attention given to the matter. Then “cerebral inhibition” took place and she broke down.
20. _Colour-photography and Photographs of Mars_
There were admirable photographs of wild birds and their nests, and of insects and plants in this exhibition. I saw the new Lumière coloured transparent photographs thrown by a lantern on the screen, and could distinguish the dots of red, green, and violet colour on what, at a little distance, appeared to be a brilliantly white part of the picture (the shirt collar of a “sitter”), just as one sees a mosaic of coloured dots in the blazing sunlight of the pictures painted by the French school of so-called “vibristes” (Monod and others). Perhaps the most remarkable of these photographs was a set of prints from untouched photographs of the planet Mars, executed in July 1907 by Professor Perceval Lowell at his observatory in Arizona.