Primarily, the conquest of the Isthmian barrier was the conquest of the mosquito. Not mountains to be leveled, nor wild rivers to be tamed, nor yet titanic machinery to be installed, presented the gravest obstacles to the canal builders. Their most feared enemies were none of these, but the swarms of mosquitoes that bred in myriads in every lake, in every tiny pool, in every clump of weeds on the rain-soaked, steaming, tropical land. For these mosquitoes were the bearers of the dread germs of yellow fever and of malaria; and the conditions that encouraged their multiplication bred also typhoid and all manner of filthy disease. Each mosquito was a potential messenger of death. The buzzing, biting pests had defeated the French in Panama without the French ever having recognized the source of the attack. It was because the Americans, thanks to Great Britain and to Cuba, knew the deadly qualities of the mosquitoes that they were able to plan, under the leadership of Col. W. C. Gorgas, a sanitary campaign of unprecedented success. It achieved two victories. One was that it made of the Canal Zone the most healthful strip of land under tropic skies. The other is the Panama Canal.When one looks about in an effort to place the credit for these great sanitary achievements he must go back to Cuba, where the yellow fever commission, consisting of Reed, Carroll, Lazear, and Agrimonte, made the remarkable investigations proving that yellow fever is transmissible only through the bite of a mosquito. He must go still further back to Maj. Roland Ross of the British Army, and his epoch-making discovery that malaria is conveyed only by the bite of another kind of mosquito. And, if he is just to all who have contributed to the establishment of the insect-bearing theory of disease, he must not forget Sir Patrick Manson who first proved that any disease could be transmitted by insect bites. It was he who discovered that filariasis is transmissible by this method alone. It was from him that Ross gathered the inspiration that is releasing humanity from one of the most insidious of all the diseases to which mortal flesh is heir. And it was from Ross's malaria discoveries, in turn, that Reed carried forward to successful proof the theory which had persisted in some quarters for generations that yellow fever was transmissible through mosquitoes; a theory already partially proved by Dr. Carlos Finley, of Havana, 20 years earlier.

But all of the surmises and theories came short of the truth until Reed, Carroll, Lazear, and Agrimonte (Lazear at the cost of his life and Carroll at the cost of a nearly fatal attack of yellow fever) took up the work of proving that there was only one way in which yellow fever could be transmitted; namely, by the bite of the mosquito. Sleeping with patients who had yellow fever, wearing the clothes of those who had died from it, eating from utensils from which yellow fever victims had eaten—in short, putting to the most rigid test every other possible method of infection, they proved by every negative test that yellow fever could not be produced in any way other than by the bite of a mosquito.

The next step was to give affirmative proof that yellow fever was caused by the bite of the female "stegomyia"—she of the striped stockings and the shrill song. This meant that someone had to have enough love for humanity to risk his life by inviting one of the worst forms of death to which human flesh is heir. Those doctors knew that they could not as brave men ask others to undergo the risks that they themselves might not accept, so in a little council chamber in Havana the three Americans—Reed, Carroll, and Lazear—entered into a compact that they themselves would permit infected mosquitoes to bite them. Reed was called home, but Carroll and Lazear stood with the keen and cold eyes of scientists and saw the mosquitoes inject the fateful poison into their blood. Later, after Lazear had died and Carroll had stood in the jaws of death, soldiers of the American army in Cuba volunteered in the interest of humanity to undergo these same risks. And it was thus, at this price, that the world came to know how yellow fever is caused, and that the United States was to be able to build the Panama Canal.

After the guilt of the female "stegomyia" mosquito was firmly established the next problem was to find a method of combating her work. Dr. Reed and his associates thought that it might be done through a process of immunization, using the mosquito to bite patients with very mild cases, and after the necessary period of incubation, to transmit the disease to those who were to be rendered immune. It was soon found, however, that there was no method of transmitting a mild infection, and the next problem was to combat the work of the mosquito by isolation of yellow fever patients, and by the extermination of the mosquitoes themselves.

In Havana at this time there was another army surgeon who was destined to write his name high upon the pages of medical achievement. He was Dr. William C. Gorgas. Under the patronage of Gen. Leonard Wood, himself a physician and alive to the lessons of the yellow fever commission's investigations, Major Gorgas undertook to apply the doctrine of yellow fever prevention promulgated by the commission, and his efforts were attended with brilliant success. The result was that Havana, in particular, and Cuba, in general, were freed from this great terror of the Tropics. When President Roosevelt came to provide for the building of the Panama Canal one of his earlier acts was to appoint Dr. Gorgas the chief sanitary officer of the Canal Zone.

At first there was difficulty in establishing practical sanitation in Panama. The chief sanitary officer was then a subordinate of the commission, and, along with all of the other men who were trying to do things on the Isthmus, he found himself hindered by unsatisfactory conditions both as to supplies and as to force; consequently, his work was no more satisfactory to himself than it was to the commission or to the American people. Under these conditions an epidemic of yellow fever broke out in Panama in 1905, and it was not long before the yellow fever mosquito had seemingly established an alibi and had secured a reopening of her case before the jury of public sentiment. People, to emphasize their disbelief in the mosquito theory of the transmission of the disease, tore the screens from their doors and windows, and otherwise proclaimed their contempt for the doctors and their doctrines. This matter went so far that the Isthmian Canal Commission proposed not only a change in method but a change in personnel as well.

At this juncture Charles E. Magoon became governor of the Canal Zone, and he declared that Dr. Gorgas should have adequate financial and moral support. He was determined that the panic which the yellow fever outbreak had engendered should be halted—and a panic it was, for men rushed madly to Colon and defied the efforts of the commission, and of the captains and crews of the Panama Railroad steamships, to prevent them from returning to the States without other transportation arrangements than a determination to get aboard and stay there until the Statue of Liberty had been passed in New York Harbor. So great was this panic that Chief Engineer Stevens declared that there were three diseases at Panama: Yellow fever, malaria, and cold feet: and that the greatest of these was cold feet. The newspapers of the United States at that time quoted the poetry of such writers as Gilbert, who said:

It did not matter that in four months there were only 47 deaths on the Isthmus from yellow fever as compared with 108 from malaria in the same period—men do not stop to study mortality tables and to compare the relative fatalities of diseases when yellow fever stares them in the face.

But after all, the yellow fever panic of 1905 served a good purpose, for if the mosquito thereby secured a reopening of its case, it stirred the United States Government to give to the sanitary officers of the Canal Zone the powers they needed, and the means required to prove finally and forever in the court of last resort, the guilt of the mosquito, and to establish for once and all the method of combating its stealthy work.

The whole world recognizes the remarkable results in sanitary work that have been achieved at Panama. While it must be remembered that the population of the Canal Zone is made up largely of able-bodied men, and that, therefore, the death rate naturally would be lower than under like conditions with a normal population of infancy and old age, the fact remains that sanitary science has converted the Zone from a mosquito paradise of swamp and jungle into a region where mosquitoes have all but disappeared, and where men are as free from danger of epidemic diseases as in the United States itself.

The sanitary statistics of the Canal Zone, and of the cities of Panama and Colon, were based for several years upon an erroneous assumption of population. The Department of Sanitation estimated the population of the Canal Zone by deducting the recorded emigrants from the recorded immigrants and assumed that the difference represented a permanent addition to the Zone's population. Under this method of estimating population a serious error crept in, since hundreds of people came into Panama from the Panaman outports and were recorded as arrivals, but who, departing in small sailing vessels and launches at night after the port officers had gone home, were not recorded as having departed. In this way the sanitary department estimates of population in the Canal Zone reached a total of 93,000 in 1912. The census taken that year showed only 62,000 population in the Zone. This served to make the death rate given out by the Department of Sanitation 50 per cent lower than was justified by actual population conditions.

But one does not need to consider figures to realize what has been accomplished at Panama. Anyone who goes there and sees the remarkable evidence of the success of the efforts to conquer the disease of the tropical jungles, finds a lesson taught that is too impressive to need the confirmation of medical statistics.

The United States, after the yellow fever outbreak of 1905, never counted the cost when the health of the canal army was at stake. Not only was Uncle Sam successful in his efforts to make the Canal Zone and the terminal cities of Panama and Colon healthful places of abode, but no worker on the canal was denied the privilege of the best medical care. An average of $2,000,000 a year was expended in the prevention of sickness and the care of those who were sick. At Ancon and at Colon large hospitals were maintained where the white American and the West Indian negro had their respective wards. At Taboga a large sanitarium was maintained to assist the recuperation of those who had recovered sufficiently to leave the hospital. Besides this there were rest camps along the line for those not ill enough to be removed to the hospitals, and dispensaries where those who felt they were not in need of other medical attention could consult with the physicians and get the necessary medicines. All medical services to the employees of the Canal Commission and the Panama Railroad were free, and only nominal charges were made for members of their families. No passenger train crossed the Isthmus of Panama without carrying a hospital car for taking patients to or from the hospitals. No way station was without its waiting shed bearing the inscription: "For Hospital Patients Only." Each community had its dispensary, its doctor, and its sanitary inspector.

During the year 1912 there were 48,000 cases of sickness in the Canal Zone, of which 26,000 were white and 22,000 colored. During the same year 633,000 trips to the dispensaries were made by employees and nonemployees, divided almost evenly between white and colored. The average number of employees constantly sick in Ancon Hospital was 712; in Colon Hospital 209; and in Taboga Sanitarium 54. An average of 119 were in the sick camps all the time and 50 in the quarters. The average number of days' treatment per employee in the hospitals was a little over 14; in the sick camps a little under 3; and in quarters 2¹/₃. It cost $160,000 a year to feed the patients in the hospitals and $739,000 a year to operate the hospitals.

The work of sanitation proper cost some $400,000 a year. This includes many items. During one year about 16,000,000 square yards of brush were cut and burned; a million square yards of swamp were drained; 30,000,000 square yards of grass were cut; 250,000 feet of ditches were dug; and some 2,000,000 linear feet of old ditches were cleaned. During the same year nearly a million garbage cans and over 300,000 refuse cans were emptied. In addition to looking after the health of the Canal Zone itself, it was necessary to care for that of the cities of Panama and Colon. In the city of Panama 11,000 loads of sweepings and 25,000 loads of garbage were removed in one year; 3,000,000 gallons of water were sprinkled on the streets and as much more distributed to the poor of the city.

During one year the quarantine service, which keeps a strict lookout for yellow fever, bubonic plague, and other epidemic diseases, inspected over 100,000 passengers coming into the Zone. It required about 150,000 gallons of mosquito oil a year to keep down the mosquitoes. There are 50 known breeds of these insects on the Isthmus and perhaps some 20 species more which have not been identified. Of the 50 or more species of mosquitoes 11 belonged to the malaria-producing family—anopheles. Their cousins of the yellow-fever-producing family—the stegomyias—boast of only two species. What the other 40 or more kinds are doing besides annoying suffering humanity has not been determined. The mosquito is comparatively easy to exterminate. Its life habits are such that a terrific mortality may be produced among them during infancy. The average young mosquito, during its "wriggler" state of development, lives under the water and has to make about 8,000 trips to the surface for air before it can spread its wings and fly. If oil is poured upon the water it can get no air and death by asphyxiation follows. Two classes of larvaecide are used on the waters to exterminate the baby mosquitoes: One is an oil used to make a scum over the surface; the other a carbolic solution which poisons the water. At the head of every little rivulet and tiny, trickling stream one sees a barrel out of which comes an endless drip! drip! drip! These drops of oil or poison are carried down the stream and make inhospitable all of the mosquito nurseries of the marshes through which the waters flow. In addition to these barrels, men go about with tanks on their backs, spraying the marshy ground and the small, isolated pools of water with larvaecides.

This method of treatment has not exterminated all mosquitoes on the Isthmus, but it has so materially reduced their number that one may stay in the Zone for weeks without seeing a single one. This is a freedom, however, that must be paid for by vigilance of the most painstaking and unremitting sort. The moment the work is relaxed the mosquitoes again spread over the territory.

The United States Government will have to continue with the utmost care its work of sanitation and quarantine at Panama. If, after the canal is completed, an epidemic of bubonic plague or yellow fever should break out, it might very seriously interfere with the operation of the canal in several ways. To begin with, it would demoralize the operating force. Further than this, India and China are afraid of yellow fever because in both of these countries the stegomyia mosquito abounds. If the disease should obtain a foothold there it would be difficult to exterminate. Europe, also, might be expected to quarantine against Panama under such conditions. A 10,000-ton freighter carrying cargo through the canal would lose at least a thousand dollars for every day it was detained in quarantine by reason of having visited the canal.

A shrewd observer has said that the successful sanitation of the Isthmus of Panama is a triumph at once of medical science and of despotic government. Probably this does not overstate the case. The methods employed at Panama were arbitrary, and had to be. They probably could not be enforced at all in a democratic community in ordinary times. The people would rebel against the severity of the regulations and against the incidental invasion of their privacy. But strike any community, however free, with the fear of a swift and deadly disease and it will submit—as witness the shot-gun quarantines that used to demark the northern limits of the yellow fever zone in our own Southern States, or the despotism that governed New Orleans in the terror of 1905. At Panama this fear is ever present, so there is little danger that a responsible majority there ever would resist the sanitary work on the grounds of outraged democracy. It may be that a popular government would become careless, or inefficient, but it would not renounce the pretension. This has been proved in Cuba.

The sanitarians at Panama gave to the workers there a sense of security that contributed no little to the spirit of determination so universally remarked and commended by visitors to the Zone during the era of construction. While there was no immunity from sickness and death, yet there was no panic, no constant dread, such as destroyed the morale of the French force. The Isthmus of Panama still remained hot, its inhabitants still were forced to take the precautions that aliens must take in the Tropics; but they were inspired with a confidence that if these precautions were taken they would not be in any greater danger than if they had remained in their northern homes.

Pestilence, the scourge of the on-sweeping epidemic, the plague of swift death that is only a little worse than the panic of fear it inspires—this was the thing that was stamped out.Not since the Science of Healing opened its doors to the Science of Prevention have physicians scored a greater victory in their fight against disease and death than on the Isthmus of Panama. Not only did they help to build the canal; they demonstrated that tropical diseases are capable of human control and thereby opened up a vista of hope undreamed of to all that sweltering and suffering mass of humanity that inhabits the Torrid Zone.