The steamer remained a day at Fashoda, and then proceeded on her voyage, her next halting place being at the mouth of the Sobat, which is an effluent of the White Nile, and has its source in the mountains near the Indian Ocean. Its water is considered superior to that of the Nile for drinking purposes, and a supply was taken on board for the use of the passengers and crew.

They now entered a succession of marshes and low ground, where the river frequently divided into several channels, and was often partially blocked with great masses of weeds and other tropical vegetation. A short distance above the Sobat, Frank and Fred had their first view of a wild elephant, or rather of a troop of half a dozen or more. They were not at all disturbed by the proximity of the steamer. One was lying comfortably on the ground, and the rest stood watching the boat while it passed up the stream a few hundred yards from them. On the opposite bank of the river was a Shilluk village, and beyond it the dry grass was burning furiously and sending up a vast column of smoke. The boys were much excited over their view of the elephants, and greatly wished they could land and take a shot at the beasts. Doctor Bronson told them they would have an opportunity to hunt elephants before many days, and with this assurance they were contented.

Elephants roam the country on both banks of this part of the Nile, but they are less numerous than farther up the valley. They are hunted for their ivory by the natives, and occasionally the foreigner gets a chance at them. Every year they increase in scarcity and in shyness, so that the stranger's chance of sport among this huge game is not very good. Occasionally they visit the fields of the natives during the night, and do a great deal of damage by trampling down the crops and eating the growing plants. The Africans take advantage of their depredations to make pitfalls for them, and in this way a large elephant sometimes finds himself a prey to the hunter.

As they ascended the Nile above the mouth of the Sobat, Abdul pointed out the spot where the "sudd" formerly obstructed the river, and caused great inconvenience.

The sudd had been mentioned before, but only briefly, and one of the youths asked Abdul to describe it to them.

"From here to Gondokoro," said Abdul, "a distance of nearly eight hundred miles, you will find the White Nile running through a series of marshes and lowlands; in many places it spreads out over a wide area, and forms a large number of channels among islands of greater or less extent. You have already observed that the grass and reeds come drifting with the current, and occasionally masses of them form to such an extent that they take the shape of floating islands.

"This floating stuff sometimes becomes caught and imprisoned at low water, and it remains there, growing day by day, until the annual flood brings down so large a current that it is swept away. One year the flood was not sufficient to remove it, and it remained from one season until the next.

"Then it increased until it fairly drove the river from its bed, or rather caused it to spread out and form new channels. It became a bog, through which the water percolated or ran in unknown channels, and furnishing a foundation for masses of vegetation, that sprung up and flourished under the effect of tropical heat and moisture.

"This state of affairs continued for six or eight years, and the White Nile apparently ceased to exist, by reason of the great dam of reeds and other plants that choked the channel and made navigation impossible. This dam was the sudd of which we have been speaking.

"It remained here when Baker Pacha ascended the Nile on his expedition for the suppression of the slave trade. His advance was retarded for many months by the sudd; he was obliged to cut channels through it, and then haul his boats along from one strip of open water to another. Many of his men died from exposure and hard work in passing the sudd, and there were fears at one time that it would cause a total abandonment of the expedition.

"The sudd was full of insects, that caused great suffering to all concerned, and the air at all times was thick with mosquitoes. One of the most dreaded pests was the 'guinea worm,' that embeds itself in the feet or ankles, and produces a disagreeable and often dangerous sore. This worm is peculiar to the tropics, and is justly feared by all persons liable to its attacks. It makes a slight puncture in the skin—generally in or near the foot—and lays its eggs there. They are hatched in from two months to a year, and the puncture is so minute that its presence is not known until the eggs are developed."

One of the boys asked if the worm ever caused the death of the person attacked.

"Generally he escapes with a dreadful sore, that may be months in healing," said Doctor Bronson, who was standing near; "and not unfrequently he loses the foot or leg where the sore is developed. If the worm can be removed without breaking, and before it has created more than a small sore like a pimple, no serious harm results; but the operation is difficult, and requires great care on the part of both doctor and patient."

"How is it performed?" Frank asked.

"When the vesicle breaks," the Doctor answered, "the end of the worm shows itself and hangs outside. It is gently pulled and coiled round a piece of linen or a small stick, like a section of a toothpick, and then fastened over the wound with sticking plaster and a compress. Twice a day the performance is repeated, and as much as possible of the worm is coiled away. It takes all the way from a fortnight to three or four months to remove a worm in this way. The worms vary from six inches to three yards in length, and their circumference is about that of small wrapping twine. If a worm is broken in the process of extraction it is liable to cause inflammation, fever, deformities, loss of the limbs, mortification, and death. So you see it is not to be trifled with."

"What a terrible scourge!" said one of the boys. "I shall take good care not to go into the water in the region where this worm abounds."

"It has been known and mentioned in ancient as well as in modern writings," the Doctor continued; "and some authorities argue that the 'fiery serpents' which attacked the Israelites in the wilderness were in reality guinea worms."

"How could that be?" Fred exclaimed. "They could not be anything like serpents; and, besides, the pictures we have of the events of the Exodus show that the Israelites were bitten by something larger than the little threads you have described."

"That is quite true," was the reply; "but bear in mind that the pictures in our books were not made at the time, but many centuries afterward. The words in the original Hebrew—which are translated in our version as 'fiery serpents'—refer unmistakably to something which caused an inflammatory wound, and do not describe the serpent any farther than this. By the Greeks the Filaria, or guinea worm, was reckoned among the serpents, on account of its form as well as the results of its bite; and those who have studied the subject say that the theory is supported by the natural conditions of the country through which the Israelites passed, while the mortality among them can be accounted for by their ignorance of the proper treatment. From a scientific point of view, if not from a popular one, the subject is an interesting study."

Doctor Bronson paused, as his attention was drawn to some conical mounds on the shore near which they were passing.

"They are anthills," said the Doctor, after a brief survey. "They are made by the white ants, which are found in various parts of Africa, and display considerable skill in the construction of their homes."

The steamer halted for wood at a point close to several of the mounds, and thus gave the youths an opportunity to examine them. They found the anthills varying in height from six to ten feet, and composed of a yellowish earth, nearly as hard as brick, and quite capable of resisting the action of the rain.

Abdul said the ants used the yellow earth below the black soil on the surface. Their first move was to swallow it, and thus mix it with an albuminous matter from their bodies, so as to give it the character of cement. Then the substance was formed into the mound which rose above the level of the highest floods. When the river is low the black soil is uncovered, and the ants roam in the vicinity of the mounds; but at the time of the inundation the entire country is under water, with the exception of the mounds, which stand out like small islands.

From this point the anthills were numerous, and at the next halting place a group of antelopes was seen, with one of its number stationed on a mound as a sentry. Finding the boat would be there a sufficient time to permit the experiment, Doctor Bronson determined to capture the sentinel, as an addition to the table of the steamer. Armed with his rifle, he started on foot, carefully keeping several anthills in range of the one where the sentry was standing, and never allowing himself more than a glimpse of the creature's horns.

The sentinel did his duty thoroughly, and gave the Doctor no little trouble to approach without being discovered. Creeping slowly from hill to hill, he at last reached one about two hundred yards from that where the sentinel stood. The animal was motionless, with the exception of his head, which he turned from side to side occasionally, so as to take in the entire horizon. His side was toward his enemy, so that he offered an excellent mark. The rest of the herd was grazing near; but as the sentinel was larger and a better prize than any of his companions, the Doctor made no change of intention, and took aim at the one he had first marked as his own.

The shot had its effect. As the smoke cleared away the antelope sunk to its knees for an instant, and then rolled to the ground, where it lay, quite dead. The balance of the herd fled, and the hunter, after reloading his rifle, ran forward to survey the effect of his shot.

Mounting to the summit of the anthill, he waved his handkerchief three times, which had been agreed upon to announce a successful shot. As soon as the signal was seen four men were sent from the boat to carry away the game. The boys walked out to meet the Doctor and congratulate him on his morning's work, and also to see the dead korrigum antelope. Frank pronounced him "a beauty," and Fred said he was the finest animal of the kind he had ever seen.

"His scientific name is Damaliscus lunatus," said Doctor Bronson, "and he belongs to the family Bovidae, of which there are many varieties. Africa has more of them than the rest of the world together, and they surpass all others in beauty and numbers. There are no antelopes in Madagascar or Australia. There are a few varieties in Asia, and only one each in Western Europe and America. Look at the one I have just killed; it will weigh at least four hundred pounds when dressed, and if you measure him at the shoulder, as you would a horse, you will find he is nearly five feet high. I doubt if anyone ever saw so large an antelope as this in America."

Frank made note of the fact that the prize which had fallen to the Doctor's rifle had a skin which glistened like that of a carefully-kept horse, and was in excellent condition. The face and ears were black, and there was a strip of black along the shoulder and down the back and legs. The tail was longer than that of the American antelope, and had a tuft of hair at the end.

After looking at the antelope, and seeing him dressed and quartered, the boys tried to break into one of the anthills, in order to examine the interior. They found it nearly as hard as stone, and as they had brought no pickaxes or other digging tools from the steamer, they soon abandoned the effort. Abdul said they would find the inside full of passages, leading to a chamber in the center, where the ants made their home during the season of floods. The ants are divided into workers, soldiers, and idlers, and thus Frank thought they evinced an affinity with the human race. Doctor Bronson told him the workers were much more numerous than the soldiers; the latter were five or six times as large as the workers, and had powerful jaws, with which they could bite severely.

Fred asked if these ants were "slave makers." He had read of slave making ants, and thought, naturally enough, that in the land of the human slave hunter and slave owner the ants might follow the example of their human counterparts.

"These are not the slave makers," was the reply, "or at any rate it has not been clearly demonstrated that they indulge in the practice of maintaining involuntary servants. The one known as a slave maker is a red ant, somewhat smaller than the one before us. His habits have been studied, so that there is no doubt of his slave holding propensities.

"These red ants go out in large numbers and make war upon a species of black ant that lives in the same region with themselves. When they have conquered the settlement, they invade the nest of their victims and carry away the eggs or cocoons containing the undeveloped young; these they transport to their own nest, and they also take along a sufficient number of the black ants to take care of the young as they are hatched. It is exactly the same as if a party of slave hunters should invade an African village and carry off all the infants they could find, together with enough of the African women to feed and care for the young prisoners. The captive ants hatched in the nest become slaves as soon as they are large enough to work, and whether the old ones are retained when the children no longer require their attention has not been ascertained."

"What a curious piece of information!" exclaimed one of the boys. "It sounds like a fiction, but I suppose the naturalists have removed all doubts concerning it."

"Yes," answered Doctor Bronson; "you can read of it in any work on natural history where the habits of ants are set forth."

By the time they reached the boat she was ready to move on, and in a little while the scene of the antelope hunt was left behind.

In this part of the Nile few sailing or other boats were seen. Occasionally the natives were on the water with their canoes or their rafts of reeds, such as we have already seen, but they almost invariably propelled these diminutive craft by means of oars. Once in a while the boat of a trader from Khartoum was passed, and in one place a dozen or more of these craft were assembled in front of a native village. Abdul said they were probably awaiting the arrival of a convoy of ivory from the interior, and it might be they were taking in a few slaves, in addition to the other products of the country.

But though there was a scarcity of boats and other signs of commerce there was no lack of animal life. Frank was looking out from the deck of the steamer as it turned a bend in the river; suddenly he saw a large animal not twenty yards away, standing where it had apparently been drinking, at the edge of the river. As it caught sight of the boat it sprung up the bank and disappeared in the thicket, giving vent to an angry roar as it moved away.

"That was a lion," said Abdul, who happened to be looking in the same direction, "and you will see more of his race as we proceed. Lions are quite numerous in this part of the country, and in fact all over Africa, and if you want to hunt them you can easily do so. And there are leopards and other carnivorous animals here," he continued, "and several varieties of serpents."

Fred asked if they were in the region of the huge pythons, that were said to be large enough to swallow a man.

"We are not quite far enough for that," was the reply, "but you might see some very good ones here if you went to the snaky localities. Serpents ten or fifteen feet long exist here, but you must go nearer the equator to find them of twenty feet.

"The natives say that a man should always cross his legs like a figure four when he goes to sleep at night, otherwise he is liable to be swallowed by a python. He is said to do his work so quietly that he does not wake his victim, and can only be foiled in his attempt when the man crosses his legs as I have described, and prevents both feet being taken in at once."

"If you want a good story of an adventure with a snake," said Frank, "let me tell you of Colonel Long's experience as he narrates it."

Fred agreed to be a good listener, and so Frank settled into his chair and began the thrilling tale:

"Colonel Long says he was one day seated in his camp at Foueira, near the borders of the Albert N'yanzi, when he saw several men approaching with what he at first supposed was the trunk of a tree. It proved to be a large boa constrictor, or python, which had just been killed close to the hut where he slept at night. It measured thirty feet in length, and in diameter was the size of a child. One of his men had said that a huge snake came every night to suck the cows in the camp; but the colonel had taken the narrative as an apocryphal 'snake-story' and given it no attention. The night before, his men were seated around the fire in the hut next his own, and suddenly fled in terror at the sight of an enormous head looking at them from an opening in the wall of the hut, and at the same time countless small serpents were gliding at their feet.

"The cause was now apparent, the colonel says: the boa had laid its eggs on the outer wall of the hut, where they were hatched by the heat of the atmosphere, and the mother had come there to meet them at the time of their hatching. A strict and somewhat nervous watch was kept through the night, but without any result. The next morning the snake was intercepted while looking for its young, and dispatched with several charges of shot in its head and body. Colonel Long says that after that incident he went to bed every night with the thought of the possibility of being strangled in his sleep by one of these horrible visitors. Luckily, for him, and for us, there was no intimate friend of her snakeship to pay him a call and seek revenge for her death."

Fred asked if the bite of the python was poisonous. Doctor Bronson explained that the python belonged to the family of constrictors, like the black snake of New England, and its bite was harmless. "It seizes its prey with its mouth," said the Doctor, "but only for the purpose of holding it. At the same instant it throws its folds about its victim and crushes it with the immense power of its constricting muscles. Next it proceeds to cover it with saliva, and then begins the process of swallowing, which may occupy several hours.

"The swallowing is done by the contraction of the muscles of the head and neck, aided by the teeth, which hook backward, so that when anything has once entered it cannot be withdrawn. If a serpent of this species begins to swallow anything that cannot be carried down it will choke to death, and skeletons of pythons have been found with the skeletons of deer, goats, buffalo, or other horned animals, in their jaws. The horns had caused them to stick on the way, and as the snake could not let go for a fresh hold he perished by strangulation, as a punishment for his imprudence.

"Do not confound the python with the anaconda," said the Doctor, in an explanatory tone. "The python belongs to the Old World, and the anaconda to the New; the anaconda is found in Central and South America, in the region of the tropics, while the python inhabits Africa and Asia. The name 'boa' belongs to the entire family; but some of the naturalists say it does not properly include the anaconda, which is amphibious in its character, while the boa is not. However, that is a point so fine that it is hardly worth our discussion, and we are not likely to become so intimate with the snakes as to pass an opinion upon it."