1921. "In Costa Rica, 66 laborers before being treated for hookworm cultivated 563 acres of coffee monthly. After treatment they cultivated 750 acres. In India the amount of work increased 20 per cent on one estate and 50 per cent on another." 14 It is evident that man may win another great victory if he will persist in this campaign.

Typhoid Fever

A second "filth disease" which is of great importance is typhoid fever. It has been known for centuries, though long confused with typhus (a very different disease carried to man by the louse), but played no great rôle until about 1850. It is most dangerous where masses of people are gathered, as in cities having common supplies of milk and water or in army camps. In the Franco-Prussian War of 1870-1871 it is said that 10 per cent of the army had typhoid and that it caused 60 per cent of the deaths of the war. In the Boer War of 1889-1890, 8,022 died of typhoid as against 7,781 killed in battle. The United States has the doubtful honor of presenting the worst record, for in the Spanish War about one-fifth of our army contracted the disease and 86 per cent of all deaths were caused by it. At Jacksonville, Florida, in 1898 there were 4,432 cases and 248 deaths among 10,759 men.

The bacterium causing typhoid was found by Eberth in 1880, but the causal connection was not proved until 1900. In 1894 in Germany the first inoculations with dead germs of typhoid were given and the resulting immunity noted. It was ten years before this practice became general but it has been successful wherever tried. In our army such vaccination was optional in 1908-1909, but it was noted that proportionately about sixteen times as many unvaccinated soldiers were stricken as vaccinated. It was made compulsory in 1910 and in 1912 in the maneuvers there was but one case among 12,801 soldiers. For some nine years prior to compulsory vaccination the United States Army had about 351 cases annually, but in 1913 and 1914 there were but 4 and 7 cases respectively. American cities did not compare very favorably with the European in the years before the war. Thirty-three of its largest cities with a population of 31,500,000 averaged only 6.5 deaths to every hundred thousand while twenty-five of our cities with 20,000,000 inhabitants averaged 25.

Typhoid bacteria do not live indefinitely outside of the human body but they last a considerable time in cold water and I have seen a recent statement that they had been kept alive for two years in ice cream. They seldom increase in water but do increase rapidly in milk. Commonly they make their way to man through the milk and water supplies, though they may be carried directly to the table on the legs of house flies. In the light of present knowledge a typhoid epidemic is a disgrace. There is, however, constant danger because a few persons become typhoid carriers as the germs persist in their bodies, and thus they are a perennial source of danger. The death rate from typhoid is steadily falling. It was 37.4 per one hundred thousand in England and Wales from 1871-1875 and 2.3 from 1916-1920. In the United States it was 35.9 in 1900 and 7.8 in 1920. The Metropolitan Life Insurance Company has recently reported a decrease of 80 per cent in the deaths of its policyholders from typhoid since 1900.

Tuberculosis

Tuberculosis has long been one of the chief communicable diseases of the temperate parts of earth, though it has been important in all zones. In Europe and America it caused some 10 per cent of all deaths during the last century. Few families have been unaffected though some are more susceptible than others. There are two forms of the disease affecting man, the human and the bovine. The bovine type enters the human body largely in milk, for beef is seldom eaten raw. This type seems to attack children chiefly and probably does not cause tuberculosis of the lungs, consumption. A few experts still question the transfer of bovine tuberculosis to man but the prevalent opinion is as stated. The bacilli causing human tuberculosis are discharged into

160

140

Death Rate per 100,000

100

80

0

1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925

FIG. 6. DEATH RATE FROM TUBERCULOSIS IN THE UNITED STATES

REGISTRATION AREA

Death rate per 100,000: 1911, 1576; 1925, 867.

the air by the sputum of the patient and thus are inhaled by others. The bacilli will not live long in the sunlight but will survive indefinitely in dark corners of rooms, under carpets, etc. Thus tuberculosis is essentially an indoor disease and has become more dangerous as we live increasingly within four walls. It is likely that most of us have it at some time during our lives for few can escape contact with it. It is not incurable and yet there is no cure for it. If taken in time a patient will probably recover if freed from undue work and worry and given plenty of food and sunshine. The antituberculosis movement is one of the best organized of our social campaigns and the death rate from the disease is about one-half of what it was in 1900, as the chart (p. 226) indicates. It now stands sixth or seventh among the causes of death in our country. We have found no specific remedy nor have we found any serum which gives immunity or relieves an attack. Yet in 1912 Earl Mayo could write: "If the members of the medical profession were given a free hand to deal with this disease, backed by adequate provision, for the care of existing cases, tuberculosis could be practically stamped out within a single generation." 15

Cholera

There are two other diseases which might sweep over this country as great epidemics, both of which find their original home in Asia. Cholera, caused by the comma bacillus, is endemic in the valley of the Ganges and has been carried elsewhere by religious and other pilgrims. In the year 1885 it took a toll of 100,000 lives in Japan and caused a money loss of not less than $200,000,000. It has invaded Europe several times, the last being the epidemic at Hamburg in 1892 which destroyed 8,000 lives and cost some $25,000,000. This is thought to have been started by emigrants from Russia on their way to America but temporarily detained in Hamburg. In 1912, in the four days ending December 27, cholera is said to have killed 1,714 persons in Mecса, with some 10,000 pilgrims present at the time.16

Bubonic Plague

The bubonic plague has invaded America several times and there is some danger that it may find a permanent home here. Under the name "black death" it swept Europe in the fourteenth century, killing some 25,000,000 people, or one-fourth of the total population. In Manchuria in 1911 some 50,000 died of it in three months; every person stricken dying so far as is known. The bacillus producing this disease was isolated by an American, R. P. Strong. The bacillus lives in a little fur-bearing animal of Manchuria, the tarbagan, often hunted by the Chinese. If it reaches the lungs of a person it produces what is called the pneumonic plague, almost invariably fatal. Ordinarily it is transferred to man by the flea, resulting in the bubonic form. This disease was brought to San Francisco, probably by rats escaping from ships in the harbor, in 1909. In spite of considerable local opposition because of the alleged unfavorable advertising it caused, the United States authorities were able to check it promptly by destroying the local rats. The disease has reappeared since that time in New Orleans, Los Angeles, and Oakland. There is reason to fear that it may find a congenial home in the countless ground squirrels of California, and the victims of the last attack at Oakland appear to have been Italians who had been hunting these squirrels. In as much as we are aware of the danger it should be possible to avoid serious results. A serum has been found which gives considerable immunity against the disease.

ANÆSTHETICS AND GERMICIDES

Nitrous oxide was discovered in 1774 and its anæsthetic properties were soon recognized. By 1800 Sir Humphrey Davy used it on himself and in succeeding years a number of physicians employed it successfully. After Morton gave a public demonstration at the Massachusetts General Hospital in 1846 it was generally adopted and thenceforth surgery ceased to be torture. Medical and surgical practice developed rapidly during the first half of the last century