This was the bright side of the picture. Those who stood nearest to Agassiz, however, felt that the strain not only of work, but of the anxiety and responsibility attendant upon a new and important undertaking, was perilous for him. There were moments when this became apparent, and he himself felt the danger. He persevered, nevertheless, to the end of the summer, and only left Penikese when the school broke up.
In order to keep the story of this final effort unbroken, some events of great interest to Agassiz and of importance to the Museum have been omitted. In the spring the Museum had received a grant of 25,000 dollars from the Legislature. To this was added 100,000 dollars, a birthday gift to Agassiz in behalf of the institution he so much loved. This last sum was controlled by no official body and was to be expended at his own good will and pleasure, either in collections, publications, or scientific assistance, as seemed to him best. He therefore looked forward to a year of greater ease and efficiency in scientific work than he had ever enjoyed before. On returning from Penikese, full of the new possibilities thus opened to him, he allowed himself a short rest, partly at the sea-shore, partly in the mountains, and was again at his post in the Museum in October.
His last course of lectures there was on one of his favorite topics,—the type of Radiates as connected with the physical history of the earth, from the dawn of organic life till now. In his opening lecture he said to his class: "You must learn to look upon fossil forms as the antiquarian looks upon his coins. The remains of animals and plants have the spirit of their time impressed upon them, as strongly as the spirit of the age is impressed upon its architecture, its literature, its coinage. I want you to become so familiar with these forms, that you can read off at a glance their character and associations." In this spirit his last course was conceived. It was as far-reaching and as clear as usual, nor did his delivery evince failure of strength or of mental power. If he showed in any way the disease which was even then upon him, it was by an over-tension of the nerves, which gave increased fervor to his manner. Every mental effort was, however, succeeded by great physical fatigue.
At the same time he had undertaken a series of articles in the "Atlantic Monthly," entitled, "Evolution and Permanence of Type." They were to have contained his own convictions regarding the connection between all living beings, upon which his studies had led him to conclusions so different from the philosophy of the day. Of these papers, only one was completed. It was his last word upon science; the correction of the proofsheets was the last act of his working life, and the article was published after his death. In it he claimed that the law of evolution, in a certain sense as true to him as to any so-called evolutionist, was a law "controlling development, and keeping types within appointed cycles of growth." He maintained that this law acts within definite limits, and never infringes upon the great types, each one of which is, in his view, a structural unit in itself. Even metamorphoses, he adds, "have all the constancy and invariability of other modes of embryonic growth, and have never been known to lead to any transition of one species into another." Of heredity he says: "The whole subject of inheritance is exceedingly intricate, working often in a seemingly capricious and fitful way. Qualities, both good and bad, are dropped as well as acquired, and the process ends sometimes in the degradation of the type, and the survival of the unfit rather than the fittest. The most trifling and fantastic tricks of inheritance are quoted in support of the transmutation theory; but little is said of the sudden apparition of powerful original qualities, which almost always rise like pure creations, and are gone with their day and generation. The noblest gifts are exceptional, and are rarely inherited; this very fact seems to me an evidence of something more and higher than mere evolution and transmission concerned in the problem of life. In the same way the matter of natural and sexual selection is susceptible of very various interpretations. No doubt, on the whole, Nature protects her best. But it would not be difficult to bring together an array of facts as striking as those produced by the evolutionists in favor of their theory, to show that sexual selection is by no means always favorable to the elimination of the chaff, and the preservation of the wheat. A natural attraction, independent of strength or beauty, is an unquestionable element in this problem, and its action is seen among animals as well as among men. The fact that fine progeny are not infrequently the offspring of weak parents, and vice versa, points, perhaps, to some innate power of redress by which the caprices of choice are counterbalanced. But there can be no doubt that types are as often endangered as protected by the so-called law of sexual selection."
"As to the influence of climate and physical conditions," he continues, "we all know their power for evil and for good upon living beings. But there is, nevertheless, nothing more striking in the whole book of nature than the power shown by types and species to resist physical conditions. Endless evidence may be brought from the whole expanse of land and air and water, showing that identical physical conditions will do nothing toward the merging of species into one another, neither will variety of conditions do anything toward their multiplication. One thing only we know absolutely, and in this treacherous, marshy ground of hypothesis and assumption, it is pleasant to plant one's foot occasionally upon a solid fact here and there. Whatever be the means of preserving and transmitting properties, the primitive types have remained permanent and unchanged,—in the long succession of ages, amid all the appearance and disappearance of kinds, the fading away of one species and the coming in of another,—from the earliest geological periods to the present day. How these types were first introduced, how the species which have successively represented them have replaced one another, —these are the vital questions to which no answer has been given. We are as far from any satisfactory solution of this problem as if development theories had never been discussed."
In conclusion, he sketches the plan of these articles. "I hope in future articles to show, first, that, however broken the geological record may be, there is a complete sequence in many parts of it, from which the character of the succession may be ascertained; secondly, that, since the most exquisitely delicate structures, as well as embryonic phases of growth of the most perishable nature, have been preserved from very early deposits, we have no right to infer the disappearance of types because their absence disproves some favorite theory; and, lastly, that there is no evidence of a direct descent of later from earlier species in the geological succession of animals."
This paper contained the sentence so often quoted since, "A physical fact is as sacred as a moral principle. Our own nature demands from us this double allegiance." This expressed the secret of his whole life. Every fact in nature was sacred to him, as part of an intellectual conception expressed in the history of the earth and the beings living upon it.
On the 2nd of December, he was called to a meeting of the Massachusetts Board of Agriculture at Fitchburg, where he lectured in the evening on "The structural growth of domesticated animals." Those who accompanied him, and knew the mental and physical depression which had hung about him for weeks, could not see him take his place on the platform, without anxiety. And yet, when he turned to the blackboard, and, with a single sweep of the chalk, drew the faultless outline of an egg, it seemed impossible that anything could be amiss with the hand or the brain that were so steady and so clear.
The end, nevertheless, was very near. Although he dined with friends the next day, and was present at a family festival that week, he spoke of a dimness of sight, and of feeling "strangely asleep." On the 6th he returned early from the Museum, complaining of great weariness, and from that time he never left his room. Attended in his illness by his friends, Dr. Brown-Sequard and Dr. Morrill Wyman, and surrounded by his family, the closing week of his life was undisturbed by acute suffering and full of domestic happiness. Even the voices of his brother and sisters were not wholly silent, for the wires that thrill with so many human interests brought their message of greeting and farewell across the ocean to his bedside. The thoughts and aims for which he had lived were often on his lips, but the affections were more vivid than the intellect in these last hours. The end came very peacefully, on the 14th of December, 1873. He lies buried at Mount Auburn. The boulder that makes his monument came from the glacier of the Aar, not far from the spot where his hut once stood; and the pine-trees which are fast growing up to shelter it were sent by loving hands from his old home in Switzerland. The land of his birth and the land of his adoption are united in his grave.