Neither discomfort, however, nor danger prevented Wrangell from undertaking a third excursion in the following spring. He had great difficulty in procuring the necessary dogs, a disease which raged among them during the winter having carried off more than four-fifths of these useful animals. At length his wants were supplied by the people of the Indigirka, where the sickness had not extended, and on March 14, 1822, he again set out for the borders of the Polar Sea. During this expedition a large extent of coast was accurately surveyed by Wrangell, who sent out his worthy assistant Matiuschkin, with two companions, in an unloaded sledge, to see if any farther advance could be made to the north. Having accomplished ten versts, Matiuschkin was stopped by the breaking up of the ice. Enormous masses, raised by the waves into an almost vertical position, were driven against each other with a dreadful crash, and pressed downward by the force of the billows to re-appear again on the surface covered with the torn-up green mud which here forms the bottom of the sea. It would tire the reader were I to relate all the miseries of their return voyage; suffice it to say that, worn out with hunger and fatigue, they reached Nishne-Kolymsk on May 5, after an absence of fifty-seven days. Such sufferings and perils might have excused all further attempts to discover the supposed land in the Polar Sea, but nothing daunted by his repeated failures, Wrangell determined on a fourth expedition in 1823, on which he resolved to start from a more easterly point. On reaching the coast, the obstacles were found still greater than on his previous visits to that fearful sea. The weather was tempestuous, the ice thin and broken. It was necessary at times to cross wide lanes of water on pieces of ice; at times the thin ice bent beneath the weight of the sledges, which were then saved only by the sagacity of the dogs, who, aware of the danger, ran at their greatest speed until they found a solid footing. At length, about sixty miles from shore, they arrived at the edge of an immense break in the ice, extending east and west farther than the eye could reach.