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DR

R. WOLLASTON being appointed to read the last Croonian lecture, comanenced his discourse, by observing that the remarks which he had to offer on the occasion might be thought to bear too little direct relation to each other for insertion in the same lecture, yet that any observation respecting the mode of action of voluntary muscles, and every enquiry into the causes which derange, and into the means of assisting, the action of the heart and blood-vessels, must be allowed to promote the design of Dr. Croone, who had instituted these annual disquisitions. He accordingly divided his discourse into three parts: viz. on "duration of voluntary action;" on "the origin of sea-sickness," as arising from a simple mechanical cause, derang. ing the circulation of the blood; and then he endeavours to explain the advandage derived from riding, and other modes MONTHLY MAG. No, 204,

the

of gestation, in assisting the health under various circumstances, in preference to every species of actual exertion.

In speaking of the duration of muscu lar action, he observes, that besides the necessity of occasional intermissions from a series of laborious exertions, and the fatigue of continuing the effort of any one voluntary muscle without intermission, which are obvious to every person, there is a third view of the subject, viz. that each effort, though apparendy single, consists in reality of a number of contractions repeated at extremely short intervals, so short that the intermediate relaxatious cannot be visible, unless prolonged beyond the usual limits by a state of partial or general debility. The existence of these alternate motion, he infers from a sensation perceptible upan inserting the extremity of the finger into the ear, because a sound is then perceived which resembles that of carriages at a distance passing rapidly over a pavement, 2 L

and

and their frequency he estimates at twenty or thirty in a second; and he adds that the resemblance of the muscular vitrations to the sound of carriages at a distance, arises not so much from the quality of the sound as from an agreement in frequency with an average of the tremors usually produced by the number of stones in the regular pavement of London pass ed over by carriages moving quickly. If the number of vibrations he twentyfour in a second, and the breadth of each stone be six inches, the rate of the carriage would be about eight miles in an hour, which agrees with the truth of the facts on which the estimate is founded.

The doctor was led to the investigation of the cause of sea-sickness from what he himself experienced in a voyage. He first observed a peculiarity in his mode of respiration, evidently connected with the motion of the vessel: that his respirations were not taken with the accustomed uniformity, but were interrupted by irregular pauses, with an appearance of watching for some favourable opportunity for making a succeeding effort; and it seemed as if the act of inspiration were in some manner to be guided by the tendency of the vessel to pitch with an uneasy motion. This action, he thought, affected the system by its influence on the motion of the blood, for, at the same instant that the chest is dilated for the reception of air, its vessels become also more open to the reception of the blood, so that the return of blood from the head is more free than at any other period of complete respiration. But by the act of expelling air from the Jungs, the ingress of the blood is so far obstructed, that when the surface of the train is exposed by the trepan, a succes sive turgescence and subsidence of the brain is seen in alternate motion with the different states of the chest. Hence, perhaps, in severe head-aches a degree of temporary relief is obtained by occasional complete inspirations: in seasickness also the act of inspiration will have some tendency to relieve, if regulated so as to counteract any temporary pressure of blood upon the brain. The principal uneasiness is felt during the subsidence of the vessel by the sinking of the wave on which it rests. It is during this subsidence that the blood has a tendency to press with unusual force upon the brain. This fact is elucidated by reasoning, and by what is known to occur in the barometer, which, when carried

out to sea in a calm, rests at the same height at which it would stand on the shore; but when the ship falls by the subsidence of the wave, the mercury is seen apparently to rise in the tube that contains it, because a portion of its gravity is then employed in occasioning its descent along with the vessel; and ac cordingly, if it were confined in a tube closed at bottom, it would no longer press with its whole weight upon the lower end. In the same manner, and for the same reason, the blood no longer presses down wards with its whole weight, and will be driven upwards by the elasticity which before was merely sufficient to support it. The sickness occasioned by swinging may be explained in the same way. It is in descending forwards that this sensation is perceived; for then the blood has the greatest tendency to move from the feet towards the head, since the line joining them is in the direction of the motion, but when the descent is back. wards, the motion is transverse to the line of the body, it occasions little inconvenience, because the tendency to propel the blood towards the head is inconsi derable. Dr. Wollaston thinks that the contents of the intestines are also affect ed by the same cause as the blood; and if these have any direct disposition to regurgitate, this consequence will be in no degree counteracted by the process of respiration. "In thus referring," says our author," the sensations of sea-sickness in so great a degree to the agency of mere mechanical pressure, I feel confirmed by considering the consequence of an opposite motion, which, by too quickly withdrawing blood from the head, oc casions a tendency to faint, or that ap proach to fainting which amounts to a momentary giddiness with diminution of muscular power. At a time when I was much fatigued by exercise, I had occasion to run to some distance, and seat myself under a low wall for shelter from a very heavy shower. In rising suddenly from this position, I was attacked with such a degree of giddiness, that I involuntarily dropped into my former posture, and was instantaneously relieved by return of blood to the head, from every sensation of uneasiness. Since that time, the same affection has frequently occur. red to me in slighter degrees; and I have observed that it has been under similar circumstances of rising suddenly from an inclined position, after some degree previous fatigue, sinking down again im

nicdiately

mediately removes the giddiness; and then by rising a second time more gradually, the same sensation is avoided." In his observations on the salutary ef. fects of riding, &c. Dr. Wollaston observes, that although the term gestation is employed by medical writers as a general terin comprehending riding on borseback, or in a carriage, yet he sus pects that no explanation has yet been given of the peculiar advantages of external motion, nor does he think that the benefits to be derived from carriage-exercise have been estimated so highly as they ought. Under the term exercise, active exercise has too frequently been confounded with passive gestation, and fatiguing efforts have been substituted for motions that are agreeable, and even invigorating, when duly adapted to the strength of the invalid, and the nature of bis indisposition. His explanation of the effects of external motion upon the circulation of the blood is founded upon a part of the structure observable in the venous system. The valves allow a free passage to the blood, when propelled forward by any motion that assists its progress; but they oppose an immediate obstacle to such as have a contrary tendency. The circulation is consequently helped forward by every degree of gentle agitation. The heart is supported in any laborious effort; it is assisted in the great work of restoring a system, which has recently struggled with some violent attack; or it is allow ed as it were to rest from a labour to which it is unequal, when the powers of life are nearly exhausted by any lingering disorder. In the relief thus afforded to an organ so essential to life, all other vital functions must necessarily participate, and the offices of secretion and assimilation will be promoted during such Comparative repose from laborious exerzion. Even the powers of the mind are, in many persons, n.anifestly affected by these kinds of motion. It is not only in cases of absolute deficiency of power to carry on the customary circulation, that the beneficial effects of gestation are felt, but equally so, when comparative inabi lity arises from redundancy of matter to he propelled. When, from fullness of blood the circulation is obstructed, the whole system labours under a feeling of agitation, with that sensibility to sudden impressions which is usually termed nervousness. The mind becomes incapable of any deliberate consideration, and is impressed with horrors that have no

foundation but in a distempered imagi nation. The composed serenity of mind that succeeds to the previous alarm, is described by some persons wish a degree of satisfaction that evinces the decided influence of the remedy. Dr. Wollaston quotes a very striking fact in justification of his theory; and adds, "If vigour can in any instance be directly given, a man may certainly be said to receive it in the most direct mode, when the service of impelling forward the circulation of his blood is performed by external means. The first mover of the systems is thereby wound up, and the several subordinate operations of the machine must each be performed with greater freedom, in consequence of this general supply of power." In many cases (he further observes), the cure of a patient has been solely owing to the external agitation of his body, which must be allowed to have had the effect of relieving the heart and arteries from a great part of their exertion in propelling the blood, and may therefore have contributed to the cure by that means only. Different degrees of exer cise must be adapted to the different degrees of bodily strength; and in some cases, a gentle, long-continued, and perhaps incessant, motion may be requisite; and, in these circumstances, sea voyages have sometimes been attended with remarkable advantage.

It will be recollected by our readers, that a young man in the autumn of last year, went into a room in which were two healthy rattle snakes, and that after teasing them some time, one of them hit him, of which wound he fingered from the 17th of October till November 4th, when he died. Mr. EVERARD HOME, who attended the man through his sufferings, has laid before the Royal Society a most accurate and minute statement of the symptoms that occurred, and of the means made use of to avert the evil. After this, he refers to several other cases sent from India to Dr. Patrick Russell, and to an experiment which he made in the year 1782, while on the island of St. Lucia from all which he infers, that the effects of the bite of a snake vary accord ing to the intensity of the poison. When it is very active, the local irritation is so sudden and so violent, that death soon takes place, but the only alteration of structure of the body is in the parts close to the bite, where the cellular membrane is completely destroyed, and the neighs bouring muscles very considerably inflained. When the poison is less intense,

the