always sufficed to kill Amœbæ, Monads, Euglenæ, Desmids, Rotifers, Nematoids, and other minute aquatic organisms. The writer did not try to ascertain what was the lowest temperature which would prove fatal to these organisms, though this has been done by other observers. Spallanzani, for instance, ascertained that Ciliated Infusoria, Waterfleas, Leeches, Nematoids, and other worm-like creatures, all perished at 107°-113° Fahr.; while Max Schultze,[1] and Kühne,[2] in part working over the same ground, have quite recently fixed the limits for such organisms at temperatures varying between 104° and 113° Fahr. At these temperatures the protoplasm entering into the formation of such organisms as well as that of the tissue-elements of higher animals was not only killed, it became coagulated and assumed the condition named by Kühne "heat-rigidity." Both Max Schultze and Kühne also found that the protoplasm of plant-cells with which they experimented was always similarly killed and altered by a very brief exposure to a temperature of 1181⁄2° Fahr. as a maximum. All accurate new observations, therefore, go to prove that different kinds of living matter, whether in the form of germ or of developed organism, are killed by a brief exposure in the moist state to a temperature at or below 140° Fahr.
2. So far I have been referring to the influence of heat upon living matter when it is suddenly applied to an altogether unaccustomed extent. This is the mode of operation with which we are especially concerned, as, with the view to the interpretation of experiments on the Origin-of-Life question, we wish to know the effects of great heat upon organisms accustomed to ordinary atmospheric and aquatic temperatures. On the other hand, it should be pointed out that organisms have been found living in hot springs at temperatures very considerably above those I have just been quoting; although the very highest of the temperatures, under the influence of which living things have been reported as existing in thermal springs, is still a few degrees below the boiling-point of water. The various observations that have been made upon this subject have been collected and criticised with much care by Prof. Jeffries Wyman,[3] to whose paper I would refer the reader. The most remarkable instances of this kind, in which Confervæ, or allied organisms, have been met with—that is, the highest temperatures cited which are at all trustworthy—are thus summarized by Prof. Wyman: "The statements we have quoted," he says, "give satisfactory proof that different kinds of plants may live in water of various temperatures, as high as 168° Fahr., as observed by Dr. Hooker in Sorujkund; 174° as observed by Captain Strachey in Thibet; 185° as observed by Humboldt in La Trinchéra; 199° as observed by Dr.
