XIII

CUSANUS AND THE FIRST SUGGESTION OF LABORATORY METHODS IN MEDICINE

As illustrating how, as we know more about the details of medical history, the beginnings of medical science and medical practice are pushed back farther and farther, a discussion in the Berliner klinische Wochenschrift a dozen years ago is of interest. Professor Ernest von Leyden, in sketching the history of the taking of the pulse as an important aid in diagnostics, said that John Floyer was usually referred to as the man who introduced the practice of determining the pulse rate by means of the watch. His work was done about the beginning of the eighteenth century. Professor von Leyden suggested, however, that William Harvey, the English physiologist, to whom is usually attributed the discovery of the circulation of the blood, had emphasized the value of the pulse in medical diagnosis, and also suggested the use of the watch in counting the pulse. Professor Carl Binz, of the University of Bonn, commenting on these remarks of Professor von Leyden, called attention to the fact that more than a century before the birth of either of these men, even the earlier, to whom the careful measurement of the pulse rate is thus attributed as a discovery, a distinguished German churchman, who died shortly after the middle of the fifteenth century, had

suggested a method of accurate estimation of the pulse that deserves a place in medical history.

This suggestion is so much in accord with modern demands for greater accuracy in diagnosis that it seems not inappropriate to talk of it as the first definite attempt at laboratory methods in the department of medicine. The maker of the suggestion, curiously enough, was not a practising physician, but a mathematician and scholar, Cardinal Nicholas of Cusa, who is known in history as Cusanus from the Latin name of the town Cues on the Moselle River, some twenty-five miles south of Trèves, where he was born. His family name, Nicholas Krebs, has been entirely lost sight of in the name derived from his native town, which is the only reason why most of the world knows anything about that town. Cardinal Cusanus suggested that in various forms of disease and at various times of life, as in childhood, boyhood, manhood, and old age, the pulse was very different. It would be extremely valuable to have some method of accurately estimating, measuring, and recording these differences for medical purposes. At that time watches had not yet been invented, and it would have been very difficult to have estimated the time by the clocks, for almost the only clocks in existence were those in the towers of the cathedrals and of the public buildings. The first watches, Nuremberg eggs, as they were called, were not made by Peter Henlein until well on into the next century. The only method of measuring time with any accuracy in private houses was the clepsydra or water-clock, which measured the time intervals by the flow of a

definite amount of water. Cardinal Cusanus suggested then that the water-clock should be employed for estimating the pulse frequency. His idea was that the amount of water which flowed while a hundred beats of the pulse were counted, should be weighed, and this weight compared with that of the average weight of water which flowed while a hundred beats of the normal pulse of a number of individuals of the same age and constitution were being counted.

This was a very simple and a very ingenious suggestion. We have no means of knowing now whether it was adopted to any extent or not. It may seem rather surprising that a cardinal should have been the one to make such a suggestion. Cusanus, however, was very much interested in mathematics and in the natural sciences, and we have many wonderful suggestions from his pen. He was the first, for instance, to suggest, more than a century before Copernicus, that the earth was not the centre of the universe, and that it would not be absolutely at rest or, as he said, devoid of all motion. His words are: "Terra igitur, quæ centrum esse nequit, motu omni carere non potest." He described very clearly how the earth moved round its own axis, and then he added, what cannot fail to be a surprising declaration for those in the modern times who think such an idea of much later origin, that he considered that the earth itself cannot be fixed, but moves as do the other stars in the heavens. The expression is so astonishing at that time in the world's history that it seems worth the while to give it in its original form, so that it may be seen

clearly that it is not any subsequent far-fetched interpretation of his opinion, but the actual words themselves, that convey this idea. He said: "Consideravi quod terra ista non potest esse fixa, sed movetur ut aliæ stella."

How clearly Cusanus anticipated another phase of our modern views may be judged from what he has to say in" De Docta Ignorantia " with regard to the constitution of the sun. It is all the more surprising that he should by some form of intuition reach such a conclusion, for the ordinary sources of information with regard to the sun would not suggest such an expression except to a genius, whose intuition outran by far the knowledge of his time. The Cardinal said: "To a spectator on the surface of the sun the splendor which appears to us would be invisible, since it contains, as it were, an earth for its central mass, with a circumferential envelope of light and heat, and between the two an atmosphere of water and clouds and of ambient air." After reading that bit of precious astronomical science announced nearly five centuries ago, it is easy to understand how Copernicus could have anticipated other phases of our knowledge, as he did in his declarations that the figure of the earth is not a sphere, but is somewhat irregular, and that the orbit of the earth is not circular.

Cusanus was an extremely practical man, and was constantly looking for and devising methods of applying practical principles of science to ordinary life. As we shall see in discussing his suggestion for the estimation of the pulse rate later on, he made many other similar suggestions for diagnostic

purposes in medicine, and set forth other applications of mathematics and mechanics to his generation.

Many of Cusanus' books have curiously modern names. He wrote, for instance, a series of mathematical treatises, in Latin of course, on " Geometric Transmutations," on "Arithmetical Complements," on "Mathematical Complements," on "Mathematical Perfection," and on "The Correction of the Calendar." In his time the calendar was in error by more than nine days, and Cusanus was one of those who aroused sufficient interest in the subject, so that in the next century the correction was actually made by the great Jesuit mathemati- . cian, Father Clavius. Perhaps the work of Cusanus that is best known is that " On Learned Ignorance— De Docta Ignorantia," in which the Cardinal points out how many things that educated people think they know are entirely wrong. It reminds one very much of Josh Billings's remark that it is not so much the ignorance of mankind that makes them ridiculous, as the knowing so many things that ain't so. It is from this work that the astronomical quotations which we have made are taken. The book that is of special interest to physicians is his dialogue "On Static Experiments," which he wrote in 1450, and which contains the following passages:

"Since the weight of the blood and the urine of a healthy and of a diseased man, of a young man and an old man, of a German and an African, is different for each individual, why would it not be a great benefit to the physician to have all of these various differences classified? For I think that a