Sandy Lodge, Moor Park, Northwood HA6 2HT, United Kingdom
Croone was first educated at Merchant Taylors’ School.
St Andrew's St, Cambridge CB2 3AP, United Kingdom
Croone studied at Emmanuel College, Cambridge, where, after taking his first degree in arts in 1650, he was elected to a fellowship. Twelve years later he was created M.D. by royal mandate.
Croone was educated at Merchant Taylors’ School and Emmanuel College, Cambridge, where, after taking his first degree in arts in 1650, he was elected to a fellowship. Twelve years later he was created M.D. by royal mandate, and in 1674 he was made a fellow of the Royal College of Physicians.
In 1659 Croone was appointed a professor of rhetoric at Gresham College, London, where his colleagues were Lawrence Rooke, Christopher Wren, William Petty, and Jonathan Goddard. He was thus drawn into the circle of men out of whose meetings grew the Royal Society. An active interest in experimentation led to his being named “register” and involved him in planning the early program of the new society. When it received its charter in 1662, Croone became one of its first fellows, often served on its council, and remained one of the most active of its early fellows until his death.
Croone’s reports to the Royal Society dealt with a variety of subjects, but he had a particular and continuing interest in muscular action and embryology. His first experiment concerned the use of alcohol as a preservative of animal tissues. Croone may have got the idea from Boyle, who was experimenting with alcohol before 1662. There are later reports (1662-1664) recording observations on developing embryos. About that time many authors were at work on the developing chick egg. On 22 February 1672 Malpighi sent to the society a discourse on the chick embryo before and after incubation. A week later Croone stated that he had found the “rudiments of the chick in the egg before incubation” and read the first part of his paper “De formatione pulli in ovo” 2 on 14 March; Cole described it as the “first reasoned attempt, based on observation and illustration, to establish the corporeal existence of performed foetus in the unincubated egg.”
Croone had been the earliest among his contemporaries to concern himself with muscle motion. He published his essay De ratione motus musculorum in 1664, and much of the subsequent discussion on this subject was either a commentary on Croone’s views or a derivation from them. In the seventeenth century, before Croone, the ideas of muscle motion were derived from Erasistratus and Galen and represented little advance on them. Erasistratus considered that when a muscle is filled with pneuma, its breadth increases while its length diminishes; and for this reason it is contracted. Galen did not offer any mechanism to account for muscle contraction but viewed muscle as simply moved by the motor faculty that comes from the brain. To him muscle was made up of fibers and flesh, the fibers being continuous with those of the tendons at either end. Croone, while accepting Galen’s concept of the structure of the muscle as tendinous fibers and flesh, describes experiments which show that something necessary to the contraction of muscle does pass along the nerve from the brain. Although he uses the word “spirit” in considering the nature of this force, he makes it a definite material substance, “a rectified and enriched juice.” He developed the idea that the nerves or nerve membranes are in a state of tension and that the nerve impulse consists of vibrations transmitted along the nerve in the same way that vibrations are transmitted along the tightened string of a musical instrument. Croone emphasized the role that blood might play in the contraction of the muscle. Not only did he consider that the muscle contraction was brought about by the interaction of the nervous “juice” and the blood, but he also thought that the circulation of the blood within the muscle would be stimulated by its contraction. Since the muscle swelled in contraction, its artery would also necessarily be enlarged and would, therefore, offer less resistance to the inflowing blood.
When the Royal Society suspended its meetings owing to plague in 1665, Croone took the opportunity to visit Montpellier, where he met the young Danish anatomist Steno. Steno had been working at Leiden and Paris with Jan Swammerdam, who had demonstrated experimentally that muscles do not swell during contraction. Steno was thus skeptical of Croone’s theory, especially, he argued, since not enough was known about fluids contained within muscles.
On his marriage in 1670, Croone had had to surrender his professorship at Gresham College and succeeded Sir Charles Scarburgh as a lecturer in anatomy at Surgeons’ Hall. During the years that followed, he evidently continued to ponder the problem of muscle motion. Since his assumption that muscle swelled in contraction had been proved false experimentally, he sought a mechanism, that would produce contraction without swelling. He therefore suggested that instead of the whole muscle’s forming one large bladder, each individual muscle fiber formed a series of very minute bladders. This modified theory he presented in his lectures in 1674 and 1675, shaving estimated by a mathematical calculation that the smaller and more numerous the bladders were in the fiber, the smaller would be the outward swelling of the muscle in contraction. This hypothesis was similar to one advanced by Giovanni Borelli in his De motu animalium (1680-1981).
Croone made two important contributions to muscle physiology. He altered the concept of “spirits” from that of a vague and ethereal “wind” to that of a definite physical “juice” and thereby made them susceptible to observation and reason, and he introduced the idea that some sort of chemical reaction may be involved in muscle contraction. Furthermore, he suggested that nerve impulse might be a disturbance or vibration along the nerves rather than a flow of substance.
Croone married Mary, daughter of Alderman John Lorymer of London. After his death, she became the wife of Sir Edwin Sadleir, of Temple Dinsley, Hertfordshire, and died on 30 September 1706.