Within three months Cuvier fell under a stroke of paralysis, and shortly died. The day before the attack he had said to Agassiz, "Be careful, and remember that work kills." We doubt if it often kills naturalists, unless when, like Cuvier, they also become statesmen. But to live and work, the naturalist must be fed. It was a perplexing problem how possibly to remain a while longer in Paris, which was essential to the carrying on of his work, and to find the means of supplying his very simple wants. And here the most charming letters in these volumes are, first, the one from his mother, full of tender thoughtfulness, and making the first suggestion about Neuchatel and its museum, as a place where the aspiring naturalist might secure something more substantial than "brilliant hopes" to live upon; next, that from Agassiz to his father, who begs to be told as much as he can be supposed to understand of the nature of this work upon fossil fishes, which called for so much time, labor, and expense; and, almost immediately, Agassiz's letter to his parents, telling them that Humboldt had, quite spontaneously and unexpectedly, relieved his present anxieties by a credit of a thousand francs, to be increased, if necessary. Humboldt had shown a friendly interest in him from the first, and had undertaken to negotiate with Cotta, the publisher, in his behalf; but, becoming uneasy by the delay, and feeling that "a man so laborious, so gifted, and so deserving of affection ... should not be left in a position where lack of serenity disturbs his power of work," he delicately pressed the acceptance of this aid as a confidential transaction between two friends of unequal age. Indeed, the relations between the "two friends," one at that time sixty-three, and the other twenty-five, were very beautiful, and so continued, as the correspondence shows. Humboldt's letters (we wish there were more of them) are particularly delightful, are full of wit and wisdom, of almost paternal solicitude, and of excellent counsel. He enjoins upon Agassiz to finish what he has in hand before taking up new tasks (this is in 1837), not to spread his intellect over too many subjects at once, nor to go on enlarging the works he had undertaken; he predicts the pecuniary difficulties in which expansion would be sure to land him, bewails the glacier investigations, and closes with "a touch of fun, in order that my letter may seem a little less like preaching. A thousand affectionate remembrances. No more ice, not much of echinoderms, plenty of fish, recall of ambassadors _in partibus_, and great severity toward booksellers, an infernal race, two or three of which have been killed under me."