THIS _Crepitaculum caude_, as an American has called it, has been the theme of many speculations. Its origin and its use have been discussed alike by the scientific and the unscientific, nor have they even now arrived at any very definite conclusions on these two points. There are theories as to its development, its form and size, its age and its utility, the caprice witnessed in all of these adding to the romance of its history; and whether its length increases by a link annually, or on each occasion of desquamation, have been among the questions connected with it. If we believe what the American Indians declare, an additional joint to the rattle grows whenever a human being falls a victim to that particular snake—a tradition more poetical than rational. The Indians also think the rattle vibrates more in dry than in wet weather, and are therefore cautious in traversing the woods during rainy seasons. This belief has given rise to the idea that the rattle is affected by damp—a fact which was affirmed so long ago as 1722.[82] The most reasonable clue to this is, that there may be less to disturb the reptile at a time when all animated nature is to a certain extent inclined to retirement and repose; for if the reptile be disturbed, rain or no rain, the rattle vibrates. In English as well as in American scientific journals, the subject of the rattle is ever and again ventilated by physiologists, and new suggestions are thrown out. In the present chapter I will endeavour to give a sort of digest of all these theories, venturing to offer in addition the results of my own observations. Appended is a drawing of the first rattle I ever saw or had in my possession. It is associated with a delightful visit of several months to some very dear friends in Iowa, and it recalls more particularly one lovely September afternoon. We were driving along a wild country road, where the prairie on either side was radiant with its floral carpet, and where the Mississippi gleamed like a succession of lakes between the wooded and picturesque bluffs that formed the background to the east. Suddenly the horses refused to advance, and without any visible reason to _me_; but the friend who was driving us recognised, in what seemed to be merely a little dry twig in the middle of the road, nothing less than a young rattlesnake. Now, to see a rattlesnake and to hear its rattle had been the great ambition of my prairie sojourn, and as my friend threw the reins to his wife and alighted to deal a death-blow, I entreated him to spare it for a few minutes only that I might examine and hear the as yet unfamiliar appendage.