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speculations that biologists have allowed themselves concerning the origin of living substance on the earth. A speculation that is interesting only because it was suggested by a great scientific

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man-a physicist, however, not a biologist-is Lord Kelvin's theory that living substance was brought to this earth from celestial regions by meteorites. A more acceptable theory is that at some earlier geologic age the conditions of earth, atmosphere, temperature, etc., were at one time of such a favorable

nature that just that fortunate coincidence of all necessary conditions and elements occurred which allowed C, H, O, N, to unite in those great, almost infinitely complex, molecules which compose the albuminous compounds whose existence is the only real chemical characteristic peculiar to living matter. But we have already indicated that the production of such compounds would not necessarily be the production of protoplasm. What of the complex definitive physical organization of protoplasm on which we predicate so much of its capacity? The botanist Schaffhausen believes that water, air, and the necessary mineral substances have been directly combined under the influences of life and heat and have given birth to an

Fig. 36.-African or two-toed ostrich, Struth io camelus. (Photograph by William Graham.)


Fig. 37.-Opossum, Dudelphus virginiana. (One-tenth natural size; photograph by W. K. Fisher.)

uncolored protococcus which next became Protococcus riridis. 1)elage asks: “If the thing is so simple why does not the author produce one of these protococci in his laboratory? On lui jerait grâce de la chlorophylle / " Nägeli holds that when the albuminous compounds had their birth in an aqueous liquid, as they were not soluble in water, they were precipitated. This precipitate was formed of minute particles, a sort of crystal which he calls micellae. These micella are the materials from which organisms were formed. An inorganic crystal deposited in a saturated solution of the same nature determines a deposit on its surface in the form of tiny crystals, by which means it increases in size. In the same way, when some of these albuminous micellae are formed anywhere, they facilitate further precipitation within their sphere of influence in such a way that the formation of other micellae, instead of going on uniformly in the liquid mass, is localized at certain points. Thus are found aggregates of an albuminous nature which constitute the primitive protoplasm. This is Nägeli's suggestion, and Nägeli is one of the most thoughtful biologists who has ever lived Granting that protoplasm must have had a natural, spontaneous beginning on this earth, being neither brought to it from other worlds nor created extranaturally on this world, biologists indulge in some speculations as to the probable whereabouts of this first appearance of life, and as to whether living substance was formed spontaneously but once only or several times, and perhaps in several places. It is not necessary here to follow up such speculations. The only one of them with any scientific evidence at all for it is the theory that life began at the poles or perhaps particularly at the north pole. The evidence for this is based, first, on the fact that in accordance with the cosmic theory of world evolution, the poles of the earth must have been first in a condition under which life might exist, and, second, on facts revealed by the study of the geographical distribution of living and fossil organisms. There seems to be some slight scientific foundation for the claim that the first organisms lived in polar regions.

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