When Stensen, or as he is more familiarly known by his Latin name, Steno, discovered and announced the fact that the heart is a muscle, he was looked upon with very much the same suspicion as to his sanity as Harvey, a half-century before, when the great English physiologist proclaimed the circulation of the blood, and such suspicions were rather openly expressed by those who were too conservative to accept this new teaching. The heart had been considered, not figuratively as we now speak, but seriously and very literally, as the seat of the emotions. Over and over again, all men had had the experience that in times of emotional stress the heart was disturbed. They could feel their emotions welling up from their hearts, therefore there was no doubt in their minds of the truth of the old teaching. Into the midst of this perfectly harmonious concord of scientific opinion, without a dissenting voice anywhere in the world, comes a young man not yet twenty-five, who almost sacrilegiously declares that the heart is merely a muscle and not a secreter of emotions. Fortunately for him, he was of gentler disposition than most of the other men who have had the independence of mind to make discoveries, and so no very bitter opposition was aroused against him. He was considered too harmless to be taken very seriously, but at least when the announcement first came, most of those who knew anything about medicine, or thought they did, and this is much more serious in these cases, recognized that young Stensen had somehow allowed himself to be led astray into a very foolish notion, and one that could only emanate from a mind not quite capable of realizing truth as it was; and they did not hesitate to say so.
After this Stensen found the Netherlands quite an unsympathetic place for his studies, and so moved down into Italy, where he could find more freedom of thought for research and more appreciation, and continue his original investigations with less scorn for his new discoveries. Here he continued to hit upon original ideas that were likely to make things quite uncomfortable for him, not because of religious intolerance, but because of the more or less hide-bound conservatism that always characterizes mediocre minds. Far from coming into disrespect here, however, he acquired many and very close friends. He laid the foundation of modern geology and wrote a little book that is a very wonderful anticipation of supposedly nineteenth century ideas in that science. He had come down into Italy a Protestant, having been raised in that religion in his native Denmark. He found so much of sympathy with every phase of intellectual activity among the ecclesiastics in Italy, that he not only became a convert to Catholicity, but after a time a Catholic priest. His reputation spread to Rome, and the Pope not only sent for and received this innovator in anatomy and the founder of geology very courteously, but treated him with every mark of appreciation, and this within a half a century after Galileo’s condemnation. Stensen eventually went back to Northern Europe as a bishop, in the hope of being able to convert to Catholicity those among the Teutonic nations who had been led away during the religious revolt.
James J. Walsh, The Popes and Science (1908)