HEAT CONTRACTION OF ELASTIC TISSUE

(1) On heating elastic tissue (ligamentum nuchæ) there is a gradual uniform contraction as the temperature increases up to 65° C., at which point there is a rapid contraction lasting to 75° C., after which the contraction again becomes gradual. (2) The contraction at 65° C. is due to the fibrous tissue in the ligamentum nuchæ, as is shown by the heating of tendon and of digested ligamentum nuchæ. (3) The contraction of fibrous tissue is not due to a coagulation of the contained proteins, but is probably due to the conversion of collagen to gelatin, which then contracts. (4) The shortening of fresh ligamentum nuchæ on heating is perfectly reversible below temperatures of 65° C. When heated above this temperature and then cooled it shows a large amount of "persistent thermal contraction." (5) The curve of heating of digested ligamentum nuchæ shows no contraction at 65° C., and is almost perfectly reversible on cooling, there being only a small, variable amount of permanent shortening. (6) The contraction of elastic tissue by heat is a physical change similar to that undergone by stretched india-rubber under the influence of change of temperature. (7) When elastic tissue is heated in Ringer's solution there is a loss of weight, which is only partially regained (within the space of half an hour) on cooling. This loss of weight is caused by the squeezing out of water due to contraction, and is probably only an effect and not the cause of contraction.