Cause of motion sickness


Cause of motion sicknessMotions of the second class, then, have been the rule with the infant. We must now bear in mind the nature of the motion to which the child has been subjected in utero and afterwards until it has become independent in locomotion. Of this motion we must bear in mind the nature of the details, what variations and their frequency and abruptness, what amplitudes and violence of movements, what velocities, what aggregate amount of movements and of variations in given times.

He that bears in mind these details of the average case of the kind under consideration, and has a correct an experimental idea of the motions of large vessels in the broad, open ocean, and has an equally good idea of the motions of small vessels in limited channels of the sea will probably agree with me that the passive motions of the infant, pre-natal and post-natal, are more violent and complicated than the ordinary motions of the large ships on the open sea, and less violent and complicated than the motions of the small vessels on the confined seas.

Now since second-class motions have been the rule with the infant, we should expect to find what is really the case, namely, that when subjected to the more gentle motions of a large, steady ship out on the open sea, the infant does not get sea-sick, because it is the habit of its vaso-nervous mechanism to adjust to motions of that class. And on the other hand we should also expect to find what is also really the case, namely, that when subjected to the more violent motions of a small vessel on an ocean channel, the infant does get sea-sick, because it is not the habit of its vaso-nervous mechanism to adjust to motions so violent.

This vaso-nervous adjusting habit being constitutional, it remains efficient and operative for some time after the child begins to execute movements of its own determination. It is during this time that it enjoys immunity from sea-sickness under the circumstances observed by Captain Manson. And again, as the vaso­nervous adjusting habit is the more readily revived as the time elapsed since its operation is short, we can easily understand why the liability to sea-sickness is increased as the child's age is advanced. It is, perhaps, proper here to express the opinion that getting used to the ship's motions on the part of the adult, consists in a restoration of the operation of the constitutional, vaso-nervous adjusting habit of the child. And that the greater difficulty of getting used to the violent motions incidental to stormy weather, and ordinarily to channel navigation, is consistent with the belief that for this purpose the vaso-nervous adjusting habit of the child has not only to be restored, but must be amplified to a great extent, and that to such an extent it is really an acquisition of a new habit. And a very difficult habit it is to acquire, as we may judge by the,number who cannot get used to such violent motions.

The child's exemption from motion-sickness due to vascular disturbance seenis thus far explained. So far as motion-sickness is attributable to disappointment, the child's exemption is explained by the fact that it has few expectations and but little fixedness of these few expectations, and is for these reasons but little liable to disappointment, and therefore nearly free from the causes of optical vertigo. Again, young children cannot make accurate muscular adjustments; for their adjustments are not based on correct intuitions of space and weight. Correct intuitions, depending as they do upon experience, are not yet acquired. Muscular adjustments of young children are at first tentative. Disturbances of muscular adjustment are therefore not disappointing to them. They are the rule.

Dr. Beard stated that sea-sickness but rarely affects old age above sixty. Observation and inquiry compel me to differ from him. Nausea, and vomiting are not necessarily present in sea-sickness. Very often in the absence of these symptoms the patient is supposed by himself and others not to be seasick, when at the same time he suffers from one or more of about a dozen ways in which sea-sickness may manifest itself. Many persons do not confess to being sea-Sick unless they are considerably so, or unless their illness is so clearly evident to the observer that denial is useless. At sea we hear passengers say: "I am not seasick, but my stomach is out of order." or "I am not sea-sick, but have a slight headache."