364 THE POPULAR SCIENCE MONTHLY. 



Moreover, in some recent inquiries addressed to deaf-mutes upon another 

 subject, the fact was noticed that all who were insusceptible to dizzi- 

 ness on account of the impairment of their semicircular canals by dis- 

 ease reported themselves also exempt from sea-sickness. 



But the semicircular canals must not receive all the credit. The 

 viscera of the abdomen are very full of blood, and irritated in sea- 

 sickness, and this condition will cause vomiting, as shown by very 

 many experiments on animals. The intestines are attached loosely to 

 the backbone by a fold of membrane containing some very large 

 blood-vessels. Ordinarily the intestines are held up and supported in 

 place by the muscles of the abdomen, and consequently do not drag 

 too heavily on their attachment. But in sea-sickness, it is said, either 

 on account of confused messages sent to them from the irritated semi- 

 circular canals, or because of the novelty and uncertainty of the mo- 

 tions of the ship, these muscles are unable to tell when to contract and 

 when to relax, thus affording but poor support to the intestines. Con- 

 sequently by their inertia the intestines bulge forward at the end 

 of each descent of the ship, thereby stretching and irritating their 

 attachment, and in consequence the abdominal blood-vessels are 

 engorged with blood, and this condition is expressed by vomiting, 

 which is merely Nature's effort to equalize the circulation. Force is 

 lent to this view of sea-sickness by the fact that jumping from a 

 great height causes fearful nausea on reaching the ground in this 

 case also the intestines pushing forward the abdominal wall and 

 stretching their attachment. 



There is probably a minor kind of sea-sickness, caused by the mere 

 churning about of food in the stomach, irritating the nerves there as 

 they would be irritated by a dose of mustard. This is often the sort 

 experienced in small boats, and is at once relieved by vomiting. 



The power of the imagination as one of the causes of sea-sickness 

 ought not to go without some mention. Whether or not it is more 

 powerful here than in other diseases it would be hard to say, but so 

 prominent is the mental effort that Mr. Bache some years ago wrote 

 a very interesting article on the subject, in which he maintained that 

 sea-sickness was wholly of mental origin ; that the idea of motion was 

 the result of the concurrent testimony of the senses ; and that in a 

 new motion, where there was a conflict of impressions, the brain was 

 disturbed. He said that motion caused nausea in two cases 1. When 

 the motion of the observer's body is in doubt ; 2. When the motion is 

 acknowledged by the mind but the motion is not felt. But, however 

 attractive this may be, it offers us little that is tangible. Of the very 

 many other causes suggested, it seems only necessary to name the 

 prominent ones. Naylor suggested spasm of the capillaries of the 

 brain. Barris attributed it to the instability of surrounding objects. 

 Stocker thinks it largely due to a partial vacuum in the lungs. Wol- 

 laston believed it was caused by the rise and fall of blood in the 



