Imágenes de páginas
PDF
EPUB

duced from 210 to 206, and then becomes chemically indistinguishable from lead. Thorium C (212), in the same manner, yields another form of lead with the atomic weight 208, and radium C (214) a third form with the atomic weight 210. A species of lead from Ceylon, whose atomic weight is slightly different from that of ordinary lead, lends colour to these assertions, though it cannot be supposed that all the lead in nature is derived from radio-active metals of higher atomic weight.

The subject of catalysis is assuming a greater commercial importance than heretofore, it having been discovered that hydrocarbons are enabled by this means to take up additional atoms of hydrogen, and form oils, while certain oils can be hardened into fats. Thus acetylene can be changed into complex products similar to and even identical with petroleum, and according to Professor Sabatier of Toulouse, it is even possible to imitate the Galician, North American, Rumanian and Caucasian oils at will, by varying the conditions. It is not likely that this will be done on a sufficient scale to compete with these types in the market, though a considerable industry has sprung up of late, founded on a variety of the same process. Oleic acid, for example, can be made to take up two atoms of hydrogen, and becomes converted into stearic acid ; fish oils lose their smell and are turned into a hard odourless tallow. In France, the United States, and Germany, large quantities of butter substitutes and lard substitutes are made in this way. The hydrogenation is effected by spraying the oil, and compressing it with hydrogen in the presence of nickel, under suitable degrees of temperature and pressure.

Thoria is a powerful catalyst, and can change organic acids to ketones, while titanium dioxide causes certain of the fatty acids to turn into aldehydes.

At the British Association meeting Professor E. Goldstein gave an address to the chemical section on the influence of the kathode rays on the colour of metallic salts. Sodium chloride is turned brown by this agency ; potassium bromide a deep blue; sodium fluoride rose-colour, lithium chloride bright yellow, and so on. The effect is very rapid, and endures for a long time if the salt is kept dark and cold, but disappears more or less quickly under ordinary conditions. It is supposed to be due to decomposition, and both the metal and the acid radicle are concerned in the result. Similar effects have been obtained by Giesel, and also by Kreutz, who found that rock-salt, heated in the vapour of sodium or potassium, also became coloured. The changes so produced are more permanent than those produced by the kathode rays, though if the latter be allowed to act for a sufficiently long time there is less discrepancy in the results. It is interesting to note that ordinary acetic acid shows no colour change, while chloracetic acid is turned yellow, and chloral a bright yellow. Substances so acted on are sometimes phosphorescent, and the effect is due to ultra-violet rays excited by stoppage of the beta and x-rays. The therapeutic effects of kathode and x-ray treatment are no doubt dependent in some degree on these changes, and it may be possible to discover which rays are hurtful, and to cut them off.

The chemical world has been affected by the war in various ways. Thus the supply of potash from Stassfurt has ceased ; saccharine, synthetic drugs, and glass apparatus are no longer procurable from Germany, and,

most important of all, the dyeing industry is deprived of its mainstay, the aniline colours. With regard to the last, a scheme is under consideration by the Government to establish the manufacture of dyes in this countrywhich should have been its home after Perkin's discoveries—but the problem is fraught with many difficulties.

Sir James Dewar has recently been studying the composition of air from various sources with reference to rare gases contained in it, and finds that the breath expired by different individuals contains 23-52 parts per million of gases uncondensable at 20° absolute. From 2 to 20 or 30 per cent. of this is hydrogen, the amount varying with the time of day and other conditions. In ordinary city air there are, in 1,000,000 parts, about 2:6 of hydrogen, and 227 of mingled helium and neon; country air contains 22.8 of the former and .5 of the latter. With regard to permeability, helium easily passes through highly heated quartz, a power not possessed by hydrogen, though it passes easily through hot platinum. Oxygen permeates more quickly through a rubber film than hydrogen, and hydrogen than nitrogen. The occlusion of gases, the permeability of metals and the ubiquity of hydrogen add to the difficulty of these investigations, all rubber connections and greased stopcocks having to be discarded.

C. L. B.

BOTANY.

The year has seen the publication of a considerable amount of research of a detailed and specialised character, but it does not appear to have been marked by contributions of immediate general interest or of outstanding importance.

At the meeting of the British Association in Australia, the Presidential address, by Professor Bower of Glasgow, dealt partly with the history of Australian Botany from Joseph Banks, who sailed with Captain Cook in 1770, to the present day; and partly with special Australian plants on which Bower himself has worked, especially with Phylloglossum, a very primitive Lycopod, and Tmesipteris, a link between living Lycopods and fossils of the group Sphenophyllales; and other primitive Australian forms. Numerous other papers dealt with the Australian flora, etc.

Professor Lang has published the first of a series of communications describing the structure of the Quillwort, Isoetes. This is a curious plant, a distant relation of the Clubmosses (Lycopods), all of whose immediate relations appear to be extinct. This investigation of a familiar but little understood plant promises to provide a thorough explanation of its construction and a sound basis for a comparison of the stock of Isoetes with the Stigmarian bases of the fossil tree-Lycopods, whose morphology has long been a puzzle to fossil botanists.

Miss E. M. Berridge's recent account of the anatomy of the Fagacee (Beech family) is of much interest. Her observations lead her to the conclusion that the Amentiferæ (catkin-bearing trees) are not primitive, but derived from plants with large flowers. She finds the Fagaceæ connected by various links with the Rosaceæ.

Several American botanists have published investigations on the stem anatomy of flowering-plants, in which they have attempted to trace the changes that have occurred during evolution, and from which they con

[ocr errors]

clude as others have done from more general considerations, that the tree-habit is relatively primitive in flowering-plants.

Our knowledge of fossil seeds has been augmented by two important contributions. One comes from Dr. Wieland of America, whose researches in wonderfully rich material have added so much to our information on the Bennettitales; he describes yet another type of complex inflorescence, helping to build up our conceptions of the evolution of the flower. The other, by Salisbury, is a most careful and detailed account of some new fossil species of Trigonocarpon, old seeds from the Coal measures which make one realise more profoundly how complex were plant organs even in those days.

Professor Bottomley has carried a step farther his investigations on the fertilising influence of “bacterised peat," i.e. peat acted upon by the bacteria of ordinary soil. In a paper in the Proceedings of the Royal Society on “Some Accessory Factors in Plant Growth and Nutrition," he traces the increased growth of plants supplied with this fertiliser to certain organic substances of unknown nature present only in minute proportions, yet enabling the plants to make use of a larger amount of the food available in the soil. From quantitative cultural experiments he infers that wheat seedlings are able to form a certain limited amount of these substances during germination, from material present in the grain, but that after a time their rate of growth falls off considerably unless further supplies are available from without. These substances are obtained from ordinary soil, but are more plentiful in “bacterised peat" (though not in ordinary peat), so that their presence is due to bacterial activity. Professor Bottomley draws an interesting parallel with the substances that have been found necessary by Dr. Hopkins and others, likewise in minute proportions, for the growth of young animals. The diseases of beri-beri and scurvy have been traced to the lack of similar substances when the diet consists of polished rice or lacks green vegetables and fruit.

In a series of experiments Mr. F. Kidd has thrown new light on the conditions which lead to dormancy of the embryo in ripe seeds, and which must be removed if germination is to take place. Maturation involves a cessation, or at least a retardation, of the growth of the embryo, and this is shown to be the result of the accumulation of carbon dioxide in the tissues, which acts as a mild anæsthetic. In the soil, carbon dioxide is frequently present in considerable amount, especially where manure and other organic matter is being decomposed, or in the deeper layers, and under such conditions the anesthesis tends to be prolonged and germination delayed. During maturation the accumulation of carbon dioxide is due to the seed-coat becoming impermeable to it. If the seed-coat is removed the embryos, for instance, of peas can readily be induced to continue their growth without any period of rest.

Dr. W. Brenchley, working at Rothamsted with a view to the understanding of the peculiarities of certain natural soils, has found that zinc and arsenic have no stimulative effect on the growth of pea or wheat seedlings, but are toxic even in very minute proportions—a few parts per million-while boron has a small stimulating effect on growth when in very minute proportions, though it also becomes toxic when less diluted.

Knight and Priestley have begun an attempt to analyse the beneficial influence of an electrical discharge on the growth of crops, by examining its influence on the different functions of plants. Beginning with respiration, they find that an electric discharge has no appreciable effect on the rate of respiration until it is powerful enough to raise the temperature appreciably and that then the whole effect is attributable to the rise in temperature.

Professor Ewart of Melbourne has published an impressive account of researches on oxidation by organic and inorganic catalysts. He has studied the nature of the activity of enzymes responsible for oxidation in the Apple, Lemon, Maize, Parsnip, Beetroot, etc., and in view of his results controverts the generally accepted views, first promulgated by Chodat and Bach, that oxidising elements belong to several classes, differing in chemical value and their mode of action.

M. G. T.

ZOOLOGY.

Professor Arthur Dendy, President of the Zoological section of the British Association, which this year met in Australia, took as the subject of his address“ Progressive Evolution and the Origin of Species.” Darwin and Wallace established the main principle of evolution, but at the present time there is still great diversity of opinion among expert biologists as to the means by which organic evolution has been effected. Darwin and Wallace held that species originate under the influence of “natural selection "—the selection by nature of fit variations. Later, De Vries brought forward the view that species arise by sudden “ mutations” or sports, and thus not by gradual changes, and the well-known Mendelian Professor Lotsy holds that all species originate by crossing. At present, it is mainly due to the impetus gained by the introduction of experimental methods that there exists so much difference of opinion. Professor Dendy's address was an endeavour to take a general survey of the situation.

A theory of organic evolution should account for the following principal groups of facts : (1) " that on the whole evolution has taken place in a progressive manner along definite and divergent lines; (2) that individual animals and plants are more or less precisely adapted in their organisation and in their behaviour to the conditions under which they live ; (3) that evolution has resulted in the existence on the earth to-day of a vast number of more or less well-defined groups of animals and plants which we call species."

Professor Dendy seeks to explain the fact that organisms throughout nature show a slow progression by the “law of the accumulation of surplus energy.” From Jennings's work on the “Behaviour of the Lower Organisms one is led to the conclusion that the lower animals learn by experience to make the appropriate response to stimuli without having to pass through the long process of trial and error. They are thus able to perform a given action with less expenditure of energy. The same is true for higher animals, and the power of profiting by experience is apparently a fundamental property of living protoplasm. Jennings speaks of this property or principle as the “law of the readier resolution of physiological states after repetition," and this law probably lies at the root of progressive evolution. As a corollary to the principle enunciated by Jennings, the “ law of the accumulation of surplus energy” would follow. In the organism or in the egg cell, the oftener the process of absorbing foodmaterial is repeated, the easier does the process become, and thus the organism tends to accumulate surplus energy in excess of its own needs. Professor Dendy lays emphasis on a progressive accumulation of potential energy by succeeding generations of animals and plants-each generation having a slightly greater amount than the previous one-and that by means of this cumulative energy, structural progressive changes are evolved, or in other words there is progressive evolution. He holds that there takes place in nature in the stricter sense something similar to that which seems to occur in human life, when certain families rise in general well-being and prosperity through the gradual accumulation of capital in successive generations, and in virtue of this handed-on capital each later generation starts with an advantage over the previous one.

Professor Dendy also holds that the law of recapitulation, which may be stated thus, that the life-history of the individual is a recapitulation of the life-history of the race, is a logical necessity if evolution has taken place. Leaving out, for the present, the complication introduced by the union of two germ cells of separate sexes, the behaviour of the germ cell during development is conditioned by two factors, namely its own constitution and its environinent. It is now accepted that the living matter of the germ cell is continuous from generation to generation, and given the same environment, the germ cell should develop in a similar manner in succeeding generations, but with a difference arising from the “law of the accumulation of surplus energy.” The organism developing from the germ cell will have a greater capacity for responding to stimuli—it will be a slightly more capable and efficient being in each successive generation. The organism must repeat in its life-history the stages passed through by its ancestors, because at every stage there is an almost identical organism exposed to the same environment, but there will be an acceleration in the individual life-history owing to the cumulative storing of potential energy.

As in human life, however, an organism really inherits from its parents two things, namely, living protoplasm with potential energy and an appropriate environment. When we say that an organism inherits a particular character from its parents, we really mean a special feature which is handed on if the appropriate environment is also present to bring out that character. The inheritance of the environment is as im. portant as the living protoplasm, for in each life-history an animal is capturing and assimilating from the environment handed down to it from its parent.

The response which an animal makes to its environment is probably not merely purely mechanical, for Jennings has pointed out that in the case of the lower organisms, the response to stimuli is to a large extent purposive, namely that the organism has the inherent capacity of selecting those modes of response which are best for its own well-being. Those responses to stimuli may result in change of structure, and thus the evolution of the body will be adaptive and follow along definite lines. One has, however, to remember that while the germ cell may be slightly

« AnteriorContinuar »