DETERMINATION OF CRITICAL POINT OF DEATH 171 



unit-length. This, for convenience, we shall call the coefficient 

 of relaxation. But after the death-point, the sign of response 

 undergoes an abrupt change to the negative, that is, contrac- 

 tion, the coefficient of contraction being fifty per thousand, or 

 nearly twenty-four times the coefficient of relaxation. 



The next specimen whose curve (s) is given was young 

 Spirogyra of light-greenish colour. From the slight differen- 

 tiation of these simple algal forms, and from their lack at this 

 young stage of any efficient protecting envelope, we should 

 expect them to offer but feeble resistance to the effect of heat, 

 and we find the death-point lowered to 47°, that is to say, 

 13° below that of the phanerogam Datura. Along with this, 

 we find also a difference in the coefficients of relaxation and 

 contraction. The mean coefficient of relaxation was in this 

 case '001, and that of contraction 'OO/. 



Vanishing of point of inversion with age. — The older 

 specimen of Spirogyra (S'), taken from the same place, had 

 its point of inversion raised by 4°, the death-point being 

 therefore at 51° C. There is a further and interesting 

 difference as between curves for young and old specimens- 

 In the younger specimen there was produced a very consider- 

 able contraction due to rigor, and this was followed after a 

 time by the usual post-mortem relaxation. But in the older 

 specimen the rigor was relatively slight and the subsequent 

 relaxation took place much earlier. We thus see that there 

 is a great loss of contractile power in old tissues. In still 

 older specimens the contraction tends to vanish altogether, 

 and we have no line of demarcation to mark the moment of 

 transition from life into death. In connection with this, it is 

 interesting to note that, whereas the death-spasm in young 

 leaves of Mimosa is very vigorous, old leaves exhibit little or 

 no spasmodic lateral movement at death. 



Cold-rigor. — Turning from the effect caused by con- 

 tinuous rise of temperature, I shall now proceed to the con- 

 sideration of the effect produced by the reverse process of 

 continuous fall to the minimum temperature. Here also, 

 as in the case c^i the curve for rising temperature, there is a 



