Experimental morphology / by Charles Benedict Davenport.

  • Charles Benedict Davenport
Date:
1897-1899
Catalogue details

Licence: Public Domain Mark

Credit: Experimental morphology / by Charles Benedict Davenport. Source: Wellcome Collection.

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    can withstand almost any temperature.* Muller-Thitrgatj (80) found that the “succulent labellum of Phajus freezes at — 0.56° C. ; the succulent leaf of Sempervivum, at —0.7°; the potato tuber, at — 1° ; the leaf of Tradescantia mexicana, at — 1.16° ; the ivy leaf, at — 1.5°; the leaves of Pinus austri- aca, at — 3.5°; young shoots of Thujopsis, at —4°.” (Vines.) In this series of plant tissues, we see that the more succulent the tissue, the higher its ultraminimum. Possibly the reason why spermatozoa have so low an ultramaximum, despite their small size, is on account of the denseness of their protoplasm. Not all variations in ultraminimum temperature are, however, explicable upon the ground of difference in size, body-covering, or density of plasm. The interpretation of the difference in sensitiveness to cold of the honey bee (Apis melifica) and the red ant (Formica rufa), between Bombyx on the one hand and Smerinthus and Vanessa on the other, must wait for further knowledge. The question now arises, what is the cause of death in organ- isms and protoplasm which succumb to low temperatures ? With the higher animals the immediate cause is doubtless in part asphyxia resulting from a stoppage in the flowing of the frozen blood plasma, and in part the destruction of the red blood corpuscles, as well as the white, f With the simpler organisms, like planarians, Protozoa, or Tradescantia hair-cells the case is different. An insight into the changes which pro- duce death in such organisms may be gained from KUhne’s ('64, p. 101) description of the effect of a temperature of — 14° on Tradescantia hair-cells. The frozen hairs were placed in water and observed under the microscope. “ The appearance,” * Striking cases are on record of the resistance of gemmules, or “animal spores,” to cold. Thus, Weltner (’93, p. 276) saw gemmules of Spongilla fragilis frozen in an aquarium from December 26 to January 24, from the end of January to February 5, from February 20 to March 6, and from March 12 to 24 ; the intervals being occupied by thawings. Yet these gemmules produced young sponges. In other cases, a certain amount of freezing favors the subse- quent development of gemmules, e.g. those of fresh-water Bryozoa (Braem, ’90, p. 83) and the eggs of the silk-worm (Duceatjx, ’71). t Pouchet (’66, p. 18) found that when blood of the frog was let fall into a capsule at a temperature of — 15° few of the red corpuscles were uninjured. In most the nuclei had been cast out into the plasma.