564.—The power which a person in perfect health possesses freely to exercise the different senses and to perform voluntary movements is called wakefulness or the state of being awake; the absence of the power to make voluntary movements and to utilize the different senses, combined with the quietude of all of them, bears the name of sleep.
565.—In sleep the mind either stops thinking entirely of the things which have been stored up by the individual in his memory or which are well-known facts, or else it busies itself exclusively with certain ideas or with impressions that produce upon the mind, at the time, pictures almost as vivid as the actual things or occurrences which they represent would produce. The term “insomnia” is employed when it is desired to designate the latter condition of the mind, and the mental pictures thus presented produce the effect that—although voluntary motions are at the time all in abeyance, and although the mind is absolutely quiet in all other respects—there remain certain directions in which it continues to operate actively, thus producing an elevation of the spirits (i.e., a certain degree of excitement) and more or less wakefulness. Sometimes a certain number of voluntary movements are associated with these mental impressions, and this may occur in such a degree that the organs of speech and many of the joints—indeed at times all of them—are compelled to act in harmony with the mental impressions. When this degree of insomnia is reached the person so affected is called a “somnambulist.”
566.—But in sleep the distribution of the humors of the body goes on without let or hindrance; and, similarly, the circulation of the blood, the peristaltic action of the stomach, intestines and sphincters, and the respiratory movements continue their activity. This complex state of affairs—viz., the coexistence of quietude of certain parts of the body with continued motion in other parts—has made it difficult to ascertain the mechanical cause of sleep.[[7]]
In his investigations into these subjects, von Haller placed his reliance mainly on vivisections and on experiments made upon animals. “A single experiment of this nature,” he said, “is often sufficient to disprove the deceptive conclusions or views that have prevailed through a period of years.” It is to John Hunter of England, however, says Puschmann, that the greatest credit is due for the introduction of the experimental method as a means of ascertaining the truth in questions of pathology; and von Haller was unquestionably one of the first German physicians to adopt the method.
Von Haller died at Berne on December 12, 1777.
Johann Georg Zimmermann was born in 1728 at Brugg in the Canton de Berne, Switzerland. Left an orphan at the age of eighteen, and obliged without aid from outside to choose the career which he would follow, he decided to study medicine; and with this object in view he went to Goettingen, Germany, where he was received into the family of Albrecht von Haller, who was at that time a professor in the university. Five years later (1751), when he took his doctor’s degree, he chose for the subject of his thesis, at von Haller’s suggestion, the doctrine of irritability. Upon his return to Berne in 1752, he began the practice of medicine and shortly afterward accepted the position of official physician for his native town of Brugg. It was during this period of his life that he wrote those treatises which made his name famous throughout Germany, viz., “On Solitude,” Zuerich, 1756; “On Experience in the Practice of Medicine,” Zuerich, 1763 and 1767; “On National Pride,” Zuerich, 1768 (5th edition); and “On the Epidemic of Dysentery which prevailed during the year 1765,” Zuerich, 1767 (later edition in 1789).
In 1768, through the influence of Dr. Tissot, of Lausanne, he was given the appointment of Physician to the King of England at the Court of Hanover. During the last years of his life he took a great interest in political events, recognizing with remarkable foresight the approach of an immense revolution. So strong was his belief that current events pointed to the approach of such a catastrophe, and so depressing were the effects of this belief upon his naturally hypochondriac type of mind, that the last years of his life were thereby rendered most painful. He died on October 7, 1795, not long after the full effects of the Reign of Terror had developed in France.
Tissot, who had known Zimmermann well for more than forty years, has written a most interesting notice of his life and has placed a just estimate upon the value of his writings. (Dezeimeris.) Sprengel, the author of a well-known and highly esteemed history of medicine, speaks in the following terms of Zimmermann’s treatise “On Experience in the Practice of Medicine”:—
The manly and brilliant style in which it is written, its fascinating eloquence, and the special talent which the author displays in rendering marvelously clear—without at the same time robbing them of any of their accuracy—the most obscure topics, make this book of Zimmermann’s a veritable chef-d’oeuvre.... The importance of genuine experience, its difference from false or blind routine, the advantages which real erudition confers and the necessity of combining it with experience, the nature of the obstacles which an observing spirit must overcome, the absolute need of good observations and the useful qualities which they should possess, the effects of genius, and the manner in which conclusions are to be drawn by analogy and by induction—these are the questions with which the author of this classical treatise deals.