Page:Popular Science Monthly Volume 5.djvu/721

Rh objects experimented with were thus estimated, and the temperature in successive trials was mostly made to differ from that last employed by 5° R. Operating in this way, and, in the case of eggs or seeds, subsequently taking great care to place those used in the different trials under similar conditions, alike favorable for germination or development, Spallanzani obtained the following results:

Of frogs' eggs only an extremely small number developed after having been simply raised to the temperature of 131° Fahr., while not one developed which had been heated to 145° or upward. Tadpoles produced from similar eggs all perished at 111°, and the same temperature likewise proved fatal to the parent frogs from which the eggs had been derived, as well as to aquatic salamanders and to fish with which experiments were made.

Silk-worms' eggs, and the eggs of the elm-moth (Papillon de l'Orme), developed less and less frequently when successive batches were heated to temperatures approaching 144$1/2$°. When they were actually submitted to this heat, all perished, though the highest temperature followed by development is not recorded. Silk-worms themselves, as well as the caterpillars of the elm-moth, were uniformly killed as soon as the water in which they were immersed attained 108$1/2$°.

Eggs of the common blow-fly only developed in very small numbers when raised to the temperature of 135°, while all perished at 140°. The larvæ developed from these eggs all died, as those of the silkworm and elm-moth had done, as soon as the temperature of the water rose to 108$1/2$°. Other adult larvæ, of the same species with which experiment was subsequently made, perished at the same heat.

In addition, Spallanzani experimented with some aquatic organisms, though he was unable to discover, and therefore to experiment with, their eggs. Thus leeches perished at 111°, and the Nematoids known as "vinegar-eels" at 113°. Other aquatic worms were killed at 111°, while water-fleas died at 107°.

So far, therefore, Spallanzani's results were most uniform; the different kinds of eggs were killed by mere momentary exposure to a temperature of about 140° Fahr., while the animals to which they were related perished at or about 110°.

The abbé next turned his attention to the power possessed by plants and their seeds of resisting the action of heated water. These observations were conducted in the same manner, though only the roots of the plants were immersed in the water while it was being heated. The plants were afterward carefully replaced in earth. Much care was taken when the seeds were sown to keep the batches distinct from one another, and to place them as much as possible under the influence of similar conditions.

Spallanzani's first experiments were made with the seeds of the chick-pea, lentil, wheat-grass, flax, and clover. The water was heated slowly, and the seeds were taken out as soon as the desired