GRADUAL PRESSURE CHANGES. 73
conform to motor nerves in this respect. Fratscher 1 repeated these experiments, heating very gradually, by means of a lamp applied to the small bulbous end of a tube communicating with the large vase of water in which the animals were exposed, and found he could even induce rigor mortis in normal frogs by immersing only a small portion of the body in the fluid. Acid and alkali stimuli he found might also be applied so gradually as to kill the tissues without stimulating movement. The researches of W. T. Sedgwick, 2 to whose discussion of the topic the reader is referred, seem to show conclusively that in the case of heat this cannot be due to a diminished irritability of the spinal cord by reason of the heat carried into it by the blood, and that organs with a basis of protoplasm cannot so far reverse its laws as to completely lose functional power with no pre- liminary phase of increased activity.
Quite apart, however, from the question of pain- less death in such cases the problem of the gradual differentiation of sensation, though so little explored, abounds in practical and theoretical implications of great interest, and a series of determinations was be- gun here in 1884 upon the pressure-sense according to the following method : A balance, devised and made expressly for this purpose, consisted of a solid iron base and a strong brass beam seventy-two centimetres long, hung on a steel edge and sensitive enough to be far beyond the limit of differential perception with the initial weights used. Along the whole length of the beam runs an edged iron plate,
^eber continuirliche und langsame Nervenreizung; Jenaische Zeitschrift. N. F. I. 1. (1875) S. 130.
2 On the variation of reflex excitability in the frog induced by changes of temperature. Studies from the Biological Laboratory of the Johns Hopkins University, 1882. Page 385.
