640 THE POPULAR SCIENCE MONTHLY, 



results, while we leave the other as it was — we completely arrest the 

 secretion, but we allow the vessels to dilate as before. If, on the other 

 hand, we employ physostigma, we contract the vessels, but cause great 

 secretion, such secretion as is usually accompanied by dilated vessels 

 and the free flow of blood through the gland. It is evident, then, that 

 vascular changes, although usually associated with alterations in nutri- 

 tion, do not necessarily cause them ; and that, in the gland we have just 

 mentioned, changes in the tissues composing it will occur without the 

 caliber of the vessels or the flow of blood through them undergoing any 

 material alteration. 



We will now say a word about the transference of impressions. 

 Just as we may imagine the farther side of the cord passed over the 

 pulley to be divided into difi'erent strands, while the nearer side is 

 single, and as we imag;ine difi'erent results obtained by pulling upon 

 the single string by reason of those subdivisions at its farther end, so 

 we may have the nearer end of the cord subdivided into strands, wliile 

 the farther end is single, and thus we can obtain a similar result by 

 pulling any one of the strands on the nearer end. This simile may 

 serve to illustrate the way in which we may obtain a similar result by 

 irritation of various efi'erent nerves, the stimulation being conveyed 

 to the nerve-center and reflected down the same efi'erent nerve in each 

 case. For example, a small grain of sand in the eye will cause a per- 

 son to wink violently and involuntarily. In this case the impression 

 made upon the sensory nerves of the conjunctiva is transmitted up to 

 the brain, and reflected down the motor nerves of the orbicularis palpe- 

 brarum. But some time ago, after the extraction of a tooth, and while 

 the wound in the gum was healing, I observed a twitching in the corre- 

 sponding eyelid somewhat resembling that which would have been 

 caused by a grain of sand in the eye. Here, also, we have the motor 

 nerves of the orbicularis reflexly excited, but the strand, if we may so 

 term it, through which the stimulus was sent up the nerve-center was 

 not the same, for in this case it was a dental and in the other case an 

 ophthalmic branch of the fifth. With these general remarks on reflex 

 action and transference of impressions, we will now proceed to con- 

 sider some cases in which reflex action is a cause of disease. I have 

 just mentioned one instance in which intermittent spasm of a voluntary 

 muscle, the orbicularis palpebrarum, was caused by irritation of a sen- 

 sory nerve. This leads me to remark that a very important condition to 

 be borne in mind is that constant stimulation of a sensory nerve will 

 often produce clonic or intermittent, and not tonic or continuous, con- 

 traction of the muscles which it may set in action. It was observed by 

 Nothnagel that if the sciatic nerve of a frog's leg was subjected to con- 

 stant stimulation under certain conditions, the contractions which it 

 induced reflexly in the other leg were intermittent or spasmodic, but 

 not continuous or tetanic. Another instance in which voluntary mus- 

 cles are reflexly affected is seen in the acts of coughing and vomiting. 



