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e Christian Scientist would probably deny the existence of the rash and of the fever； refuse to recognize the itching and get himself into harmony with the Infinite。 Thirdly； the method of experimental medicine。
First； the conditions were studied under which the individual cases occurred。 The only common factor seemed to be certain straw mattresses manufactured by four different firms； all of which obtained the straw from the same source。
The second point was to determine the relation of the straw to the rash。 One of the investigators exposed a bare arm and shoulder for an hour between two mattresses。 Three people voluntarily slept on the mattresses for one night。 Siftings from the straw were applied to the arm； under all of which circumstances the rash quickly developed； showing conclusively the relation of the straw to the disease。
Thirdly； siftings from the straw and mattresses which had been thoroughly disinfected failed to produce the rash。
And fourthly； careful inspection of the siftings of the straw disclosed living parasites； small mites； which when applied to the skin quickly produced the characteristic eruption。
SANITATION
WHEN the thoughtful historian gets far enough away from the nineteenth century to see it as a whole； no single feature will stand out with greater distinctness than the fulfilment of the prophecy of Descartes that we could be freed from an infinity of maladies both of body and mind if we had sufficient knowledge of their causes and of all the remedies with which nature has provided us。 Sanitation takes its place among the great modern revolutions political； social and intellectual。 Great Britain deserves the credit for the first practical recognition of the maxim salus populi suprema lex。 In the middle and latter part of the century a remarkable group of men； Southwood Smith； Chadwick； Budd； Murchison； Simon； Acland； Buchanan； J。W。 Russell and Benjamin Ward Richardson； put practical sanitation on a scientific basis。 Even before the full demonstration of the germ theory； they had grasped the conception that the battle had to be fought against a living contagion which found in poverty； filth and wretched homes the conditions for its existence。 One terrible disease was practically wiped out in twenty…five years of hard work。 It is difficult to realize that within the memory of men now living； typhus fever was one of the great scourges of our large cities； and broke out in terrible epidemicsthe most fatal of all to the medical profession。 In the severe epidemic in Ireland in the forties of the last century； one fifth of all the doctors in the island died of typhus。 A better idea of the new crusade； made possible by new knowledge； is to be had from a consideration of certain diseases against which the fight is in active progress。
Nothing illustrates more clearly the interdependence of the sciences than the reciprocal impulse given to new researches in pathology and entomology by the discovery of the part played by insects in the transmission of disease。 The flea； the louse； the bedbug； the house fly； the mosquito； the tick； have all within a few years taken their places as important transmitters of disease。 The fly population may be taken as the sanitary index of a place。 The discovery； too； that insects are porters of disease has led to a great extension of our knowledge of their life history。 Early in the nineties； when Dr。 Thayer and I were busy with the study of malaria in Baltimore； we began experiments on the possible transmission of the parasites； and a tramp； who had been a medical student； offered himself as a subject。 Before we began； Dr。 Thayer sought information as to the varieties of mosquitoes known in America； but sought in vain： there had at that time been no systematic study。 The fundamental study which set us on the track was a demonstration by Patrick Manson；＇3＇ in 1879； of the association of filarian disease with the mosquito。 Many observations had already been made； and were made subsequently； on the importance of insects as intermediary hosts in the animal parasites； but the first really great scientific demonstration of a widespread infection through insects was by Theobald Smith； now of Harvard University； in 1889； in a study of Texas fever of cattle。＇4＇ I well remember the deep impression made upon me by his original communication； which in completeness； in accuracy of detail； in Harveian precision and in practical results remains one of the most brilliant pieces of experimental work ever undertaken。 It is difficult to draw comparisons in pathology； but I think； if a census were taken among the world's workers on disease； the judgment to be based on the damage to health and direct mortality； the votes would be given to malaria as the greatest single destroyer of the human race。 Cholera kills its thousands； plague； in its bad years； its hundreds of thousands； yellow fever； hookworm disease； pneumonia； tuberculosis； are all terribly destructive； some only in the tropics； others in more temperate regions： but malaria is today； as it ever was； a disease to which the word pandemic is specially applicable。 In this country and in Europe； its ravages have lessened enormously during the past century； but in the tropics it is everywhere and always present； the greatest single foe of the white man； and at times and places it assumes the proportions of a terrible epidemic。 In one district of India alone； during the last four months of 1908； one quarter of the total population suffered from the disease and there were 400；000 deaths practically all from malaria。 Today； the control of this terrible scourge is in our hands； and； as I shall tell you in a few minutes； largely because of this control； the Panama Canal is being built。 No disease illustrates better the progressive evolution of scientific medicine。 It is one of the oldest of known diseases。 The Greeks and Graeco…Romans knew it well。 It seems highly probable； as brought out by the studies of W。H。S。 Jones of Cambridge； that； in part at least； the physical degeneration in Greece and Rome may have been due to the great increase of this disease。 Its clinical manifestations were well known and admirably described by the older writers。 In the seventeenth century； as I have already told you； the remarkable discovery was made that the bark of the cinchona tree was a specific。 Between the date of the Countess's recovery in Lima and the year 1880 a colossal literature on the disease had accumulated。 Literally thousands of workers had studied the various aspects of its many problems； the literature of this country； particularly of the Southern States； in the first half of the last century may be said to be predominantly malarial。 Ordinary observation carried on for long centuries had done as much as was possible。 In 1880； a young French army surgeon； Laveran by name； working in Algiers； found in the microscopic examination of the blood that there were little bodies in the red blood corpuscles； amoeboid in character； which he believed to be the germs of the disease。 Very little attention at first was paid to his work； and it is not surprising。 It was the old story of 〃Wolf； wolf〃； there had been so many suppos