In fact, Herbert remained in an almost continuous state of drowsiness, and symptoms of delirium began to manifest themselves. Refreshing drinks were the only remedies at the colonists' disposal. The fever was not as yet very high, but it soon appeared that it would probably recur at regular intervals. Gideon Spilett first recognised this on the 6th of December. The poor boy, whose fingers, nose, and ears had become extremely pale, was at first seized with slight shiverings, horripilations, and tremblings. His pulse was weak and irregular, his skin dry, his thirst intense. To this soon succeeded a hot fit; his face became flushed; his skin reddened; his pulse quick; then a profuse perspiration broke out, after which the fever seemed to diminish. The attack had lasted nearly five hours. Gideon Spilett had not left Herbert, who, it was only too certain was now seized by an intermittent fever, and this fever must, be cured at any cost before it should assume a more serious aspect. "And in order to cure it," said Spilett to Cyrus Harding, "we need a febrifuge." "A febrifuge," answered the engineer. "We have neither Peruvian bark, nor sulphate of quinine?" "No," said Gideon Spilett, "but there are willows on the border of the lake, and the bark of the willow might, perhaps, prove to be a substitute for quinine." "Let us try it without losing a moment," replied Cyrus Harding. The bark of the willow has, indeed, been justly considered as a succedaneum for Peruvian bark, as has also that of the horse-chestnut-tree, the leaf of the holly, the snake-root, etcetera. It was evidently necessary to make trial of this substance, although not so valuable as Peruvian bark, and to employ it in its natural state, since they had no means for extracting its essence. Cyrus Harding went himself to cut from the trunk of a species of black willow, a few pieces of bark; he brought them back to Granite House, and reduced them to a powder, which was administered that same evening to Herbert. The night passed without any important change. Herbert was somewhat delirious, but the fever did not reappear in the night, and did not return either during the following day. Pencroft again began to hope. Gideon Spilett said nothing. It might be that the fever was not quotidian, but tertian, and that it would return next day. Therefore, he awaited the next day with the greatest anxiety. It might have been remarked besides that during this period Herbert remained utterly prostrate, his head weak and giddy. Another symptom alarmed the reporter to the highest degree. Herbert's liver became congested, and soon a more intense delirium showed that his brain was also affected. Gideon Spilett was overwhelmed by this new complication. He took the engineer aside. "It is a malignant fever," said he. "A malignant fever!" cried Harding. "You are mistaken, Spilett. A malignant fever does not declare itself spontaneously; its germ must previously have existed."