We saluted these hard-working physicians, and then entered the forest from which they had just emerged. A short walk brought us to the river Challuma,[332] a tributary of the Tambopata, which we waded across. Martinez told me that this was the extreme point reached by Dr. Weddell, and that he came here to see a tree of _C. micrantha_ growing. Beyond the Challuma there is no road at all, and the really serious forest work began; two hornets stinging me on the temple and back of the neck, as I forced my way through the first bush. Martinez went in front as pioneer, clearing away obstructions with his _machete_, and the rest of our little party followed. Between lordly trees of great height the ground was entirely choked up with creepers, fallen masses of tangled bamboo, and long tendrils which twisted round our ankles, and tripped us up at every step. Ten miles on open ground is only equal to one over such country as this. In many places we had to scramble through the same dense forest, along the verge of giddy precipices which overhung the river. Often we came upon tracks where a giant of the forest had fallen, bearing all before it, and finally dashing over the cliff into the river below. The Tambopata was boiling and surging over a rocky bed, at times far below us, while at others we took advantage of a short strip of rocky beach to escape the forest. Thus we struggled on until sunset, when we reached a stony beach, and encamped for the night. This had been a most fatiguing march. In some places we were a quarter of an hour forcing and cutting our way through a space of twenty yards, and the halt was most welcome. It was a wild scene as the darkness closed round: the camp-fire and Indians on the beach, the dense gloomy forest close behind, the boiling river in front, and forest-clad mountains rising up on the other side.