A narrow-gauge railway line was being built farther and farther into the interior as the land was cleared; this had been completed a distance of fifteen kilometers, and the road-bed was in course of construction for forty additional kilometres. The morning after our arrival at Porto Gallileo we proceeded to the end of the line on the daily work-train, and pitched camp on the bank of a small stream, the Rio Negro. [Illustration: A street in Buenos Aires.] [Illustration: Porto Gallileo on the Rio Pilcomayo.] Our camp was merely a rough shed built of sheets of corrugated iron supported on poles driven into the ground. The river-water was salt and unfit for use, so each morning several large jugs of fresh drinking-water were sent in from Porto Gallileo, together with a supply of provisions. All about lay marshes, swamps, and large grass-covered areas, the latter type of country predominating. The Rio Negro teemed with a species of _piranha_. They are deep-bodied and blunt-nosed, and the jaws are armed with sharp, triangular teeth. Although they grow to a length of eighteen inches in the Orinoco and some of the other large South American rivers, those we found in the Rio Negro did not exceed eight inches in length; but they travelled in enormous schools, and made up in numbers what they lacked in size. During the hours of late afternoon, when our day’s work was over, I tried many experiments with the _piranhas_. They have a bad reputation and are known to attack animals much larger than themselves, and even human beings who enter the water. Usually they are slow to attack unless their appetite has been whetted by a taste of blood from a wound; then, however, their work is done with lightning-like quickness, and unless the luckless victim succeeds in reaching the shore immediately nothing but the skeleton will remain within a very short time. If I fished with a hook and line baited with any kind of raw meat the fish would scarcely wait for the bait to sink below the surface of the water. The number caught depended entirely upon the amount of time spent in fishing. The bodies of large mammals, such as monkeys, after we had skinned them, were thrown into the stream; instantly the ravenous hordes charged the spot and tore greedily at the bloody flesh; so great were their numbers that they threw one another out of the water in their mad struggles to reach the gory repast. On several occasions I threw dead or stunned individuals of their species into the midst of the frenzied mob, but, strange to relate, they floated on the surface of the water untouched. Unplucked birds were not molested, either. A struggle in the water seems to attract the fish, but I must admit that their behavior is very erratic. While washing my hands in the edge of the stream one day a _piranha_ snapped a piece out of a finger; a few days later a man in passing over the river on a bridge dropped his purse into the water in almost the exact spot where I