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This complete acceptance of my views is both gratifying and surprising, since neither Bancroft nor Clowes ever said or demonstrated anything of the kind until after the appearance of my various papers and of the book which they review. Never before the time of these reviews has either used the terms "hydrophilic" or "lipophilic" in any of his papers on emulsification. Indeed, when I presented the importance of colloid solvates (Bancroft's "gelatinous films ") for the understanding of the stabilization of oil-in-water and water-inoil types of emulsions, at the 1916 Urbana meeting of the American Chemical Society, both gentlemen attacked my views as impossible. At that time they were following Pickering's belief that the stability of an emulsion depends upon the production of an "interfacial film" between the two liquids which, in Bancroft and Clowes's mind, when bent one way, yielded an oil-in-water type of emulsion, and, when bent the other, a water-in-oil type. Bancroft says further:

In so far as an emulsion of oil in water is stabilized by a hydrophilic colloid, there is nothing new about this.

Here Bancroft disparages as not new the very idea which he had previously declared impossible. Of course the fact that emulsifying agents emulsify has been known since mother first made mayonnaise. What mother did not know was why her methods worked. So far as I am aware neither she, nor Clowes, nor Bancroft knew that the hydrophilic properties of colloids were an important element in the matter until I pointed this out.

Clowes concludes as follows:

While the writer of this review would not charge Dr. Fischer with any deliberate intention to mislead, the obvious haste with which this somewhat pretentious work has been constructed suggests an attempt to skim the cream of a new idea in a promising field of research.

4 Martin H. Fischer and Marian O. Hooker, SciENCE, 43, 468, March, 1916; Kolloid Zeitschr., 18, 100, 1916; 18, 242, 1916.

5 See "Fats and Fatty Degeneration," p. 29, for an account of this.

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QUOTATIONS

A MEDICAL ENTENTE WITH AMERICA WE published last week an account of the very cordial reception accorded to British medicine in the persons of Sir James Mackenzie, Sir Arbuthnot Lane and Colonel Bruce by the American medical profession during the recent annual conference at Chicago. That event marks an important stage in the development of understanding and sympathy between the two countries, not only because the doctor wields in every community a large if undefined influence, but also because it is well that in the great war against disease which is now in its opening stages the two peoples should stand side by side, mutually supporting one another. American medicine has much to give, and we know that the same can be said of our own profession. The time is opportune for the

cultivation of a closer relationship than has hitherto existed, for the creation of new facilities of study, for the endowment of research fellowships on both sides of the Atlantic, and for the interchange of scientific papers and schemes of work.

Alive to the advantages to herself of a scientific entente, Germany before the war used all these means to attract American students to her universities and schools, and to send her students to American schools. A very large measure of success attended her efforts, with the result that not medicine alone, but the sister sciences of chemistry, bacteriology, sanitation and sanitary engineering reaped immeasurable benefits. In this country we have at last awakened to the vast importance of health and of all questions affecting it. Public opinion has demanded that a Health Ministry shall be called into being, and will see to it that the activities of that Ministry, when it comes, are not curtailed in its struggle with disease and ignorance and greed. Public opinion will equally insist that the knowledge gained and progress made by our American friends, who have essayed this task in a broader spirit and at an earlier date than ourselves, are fully utilized, and the support that they may be willing to afford us secured. We shall fight our battle with hands greatly strengthened if we fight it as members of a world-wide community. Disease is international. The hope of the conquest of disease lies in prevention, which must be international as well as local. In this respect no man and no community can say that they live to themselves. A badly constructed drain in a country village contaminating a source of water supply may give rise to an epidemic of great proportions, and this may conceivably be carried by hosts of one kind or another to the world's end. We hope, therefore, that a scientific entente will not stop at medicine in the narrow sense of that term. America, for example, leads the whole world in the matter of its milk supply, and our bacteriologists and social workers cannot afford to let the opportunity of help in this direction remain unimproved. Our Ministry of Health, indeed,

when formed, will be strengthened in every way by the establishment of friendly relations with the State Boards of Health that have already done so much for America. We are aware that some steps towards the development of such a policy as we suggest have lately been taken, and that other measures are in contemplation. This is satisfactory so far as it goes. But the broadest possible basis of understanding is the best basis in the circumstances, and all branches of scientific work having the public health as their object should take part in the movement.-London Times.

SCIENTIFIC BOOKS

Principles of Economic Geology. By WILLIAM HARVEY EMMONS. McGraw-Hill Book Co. 1918. Pp. 598.

66

There are two recent books with which this at once invites comparison-Lindgren's "Mineral Deposits," and Ries's Economic Geology." It is not as comprehensive as the latter, for it omits the whole of the important subjects of coal, oil and other fuels. Perhaps for this reason and to avoid confusion in title the word "Principles" is added. To the reviewer the fact that every improvement in transportation or manipulation, like the cyanide process, increases the value of the raw material and consequently lowers the grade of the material which it will pay to work, that there is a tendency to work from small quantities of high-grade material to large quantities of lowgrade material, that production is normally in an accelerated ratio, should be classed as principles of economic geology. But it would not be easy for the student to pick out these or any other economic principles. The economic data are indeed scanty and not systematic, and there is little or no attention paid to the principles of valuation.

But if the economic side is scantily handled the geologic receives much fuller treatment. In fact twenty-one out of twenty eight chapters are concerned with the classification of ore deposits in general, their structural features and sources. Particularly valuable is the summary prefixed to the earlier chapters on the different types of deposits. Chapters

17 on structural features is also valuable. Mine waters also receive better treatment than they often do. But in his argument for the importance of ascending juvenile thermal waters one might have hoped to see a comparison of the analyses of waters with those which would be obtained from the connate or meteoric waters stimulated in circulation by hot intrusives. There is a lot of sodium carbonate and sulphate in the mine waters of many regions where "alkali" is also characteristic of the surface waters, while the mine waters of other districts are quite different. It may well be that we have a mixture of waters from more than one source, and while the author rightly attributes to precipitation by mixture of solutions an importance which is often overlooked, yet it may have even greater importance.

The range of reference is rather narrow, mainly, though by no means exclusively, to the western United States. In that respect both of the other books are superior. For instance in discussion of the class of zeolitic native copper deposits no reference is made to the work of Weed and Lewis on those of New Jersey, and one might think that Keweenaw Point was unique, except for a footnote reference to White River, Alaska. With regard to the Keweenawan deposits there are a number of minor slips (p. 397). Copper veins are still of considerable importance at the Ahmeek and adjacent mines, nor was the copper obtained from veins formerly, nor at present, wholly or mainly sulphide. It is usually native, sometimes the basic arsenide, and even in the Nonesuch lode one would hardly say that the ore vas "chiefly" chalcocite. The Nonesuch mine saved only the native copper. It is noteworthy that there is no such systematic attempt to present diverging points of view fairly as is made by Ries. Compare for instance the treatment of oolitic iron ores in each. This is probably due to the origin of the book as a course of lectures. So, too, while Lawson is referred to, as to his western work, no reference is made to his Lake Superior work. Neither is Allen's declaration that the Animakie is middle Huronian con

sidered. The Keweenawan is classed without a question as pre-Cambrian.

After the extensive treatment of ore deposits, iron, copper, gold, silver, zinc and lead receive treatment in separate chapters, while all the rest of the substances are dismissed in the last hundred pages.

Two relatively new terms are protore: "lowgrade metalliferous material not itself valuable from which valuable ore may be formed by superficial alteration and enrichment," and the horsetail structure applied by Sales to divergent minor fractures. Both these seem to

be useful.

There no list of illustrations.

ALFRED C. LANE

Aquatic Microscopy.
Aquatic Microscopy. By ALFRED C. STOKES.

Fourth Edition. New York, John Wiley and Sons. 1918. Pp. 324.

The new edition of this well-known guide for beginners retains the general features of the earlier editions. Chapter XII. of the third edition, "Some Common Objects worth Examining," has been replaced by a "Synopsis of the Preceding Chapters," which is a convenient, brief key to the forms described in the book. Minor changes have been made in the text, various scientific names have been modernized, and some of the keys have been extended. The book should continue to be a favorite, not only with the young microscopist for whom it is intended, but with many zoological students and teachers as well who desire to identify quickly and easily some of the commoner aquatic organisms.

M. F. GUYER

UNIVERSITY OF WISCONSIN

SPECIAL ARTICLES ADAPTATION IN THE PHOTOSENSITIVITY OF CIONA INTESTINALIS

I

Ciona intestinalis of the Pacific Coast1 re1 These experiments; the details of which will appear later, were performed at the Scripps Institution for Biological Research at La Jolla, California. My thanks are due to Dr. Ritter and his staff for the many courtesies shown me.

acts vigorously when exposed to light. The pigmented ocelli on the oral and atrial siphons are not the sense organs concerned. Stimulation of the ocelli does not result in a reaction, and their removal in no way interferes with the sensitivity of Ciona. The receptors responsible for the light sensitivity are localized in the inter-siphonal region in an area corresponding to the neural complex of ascidians. When this spot alone is exposed to light, the resulting effect is identical with the one following total body exposure.

II

The reaction time of Ciona to light is composed of two portions. The first is a sensitization period, during which Ciona must remain exposed to the light. The second is a latent period during which Ciona need not be exposed to the light. At the end of this period it gives its characteristic reaction, though at the moment it is no longer subjected to the source of stimulation. This latent period as found by averaging many determinations on a number of animals at different intensities, is 1.76 seconds.

III

The sensitization period (or roughly speaking, the reaction time) varies inversely as the intensity of the stimulating light. Moreover, the duration of the sensitization period multiplied by the intensity of the light is constant. This means that the amount of energy (time Xintensity) required by Ciona for a reaction to light is the same for all intensities. This familiar phenomenon in the chemical effect of light (Roscoe-Bunsen rule) and signifies that the light decomposes a constant quantity of photosensitive substance before Ciona reacts to light.

is a

IV

When kept in diffuse daylight, this species does not respond to a lower intensity of light. It does react to sunlight. However, if Ciona is placed in the dark, it will become "dark adapted" after a time and will respond to an artificial light of as low as 500 candle meters

intensity. The investigation of the rate at which it becomes "dark adapted" is of considerable interest. This is found by determining the reaction time of an animal to a light of constant intensity at 15-minute intervals in the dark-room. The following is found to be true. At first the reaction time is long, then it shortens rapidly, then slowly, and finally it becomes constant.

The duration of the exposure time multiplied by the intensity of the light gives the amount of energy received. The amount of energy determines the quantity of photosensitive substance decomposed. Therefore, the extent to which the photosensitive material requires to be is changed in order to produce the same reaction during "dark adaptation," is at first large, then it decreases rapidly, then slowly, and finally it becomes constant.

The significance of this rate of change will become apparent when we shall have considered the nature of the photosensitive substance and its mode of formation.

V

Decomposition of the photosensitive material by light, presupposes the formation of this substance within the sense organ. It will simplify matters to assume that the action of the light results in the conversion of the photosensitive material into its precursor. Thus normally, and of course in the dark, the precursor (P) forms the substance (S) sensitive to light. In the light, however, S is converted back into P.

The rate of formation of the precursor from the photosensitive substance in the presence of light, has been shown to be a direct function of the amount of energy supplied by the stimulating light. The occurrence of the reaction in the opposite direction, however, must be considered in terms of the velocities of ordinary chemical reactions. The formation of the photosensitive material from its precursor is probably a reaction of the first order. For our purposes, however, it may be a reaction of even a higher order. Practically all chemical reactions have this in common: the velocity of the reaction is at first rapid, then

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The production of the photosensitive substance in the sense organ of Ciona undoubtedly takes place in this manner when the animal is placed in the dark room. It will be seen from Fig. 1 that the amount of the precursor (P) is at first large, then it decreases rapidly, then slowly, and finally it reaches a constant minimum. This is also what happens to the reaction time, and therefore to the amount of photosensitive substance broken down before a reaction can occur during the process of " dark adaptation."

Since it was assumed that the photosensitive material decomposes into its precursor, the amount of the precursor formed at each reaction during dark adaptation, runs, in general, parallel to the amount of the precursor still unused in the reaction. Therefore, in order to serve as an "inner stimulus," the quantity of precursor formed by the stimulating light must

bear a definite quantitative relation to the amount already present. This is merely the basis of the familiar Weber-Fechner concept, that the amount of stimulus necessary to produce a perceptible increase in sensory effect represents a constant fraction of the quantity of stimulus that has gone before.

VI

The crucial test of any explanation lies in its ability to predict the course of events. Such a test was applied to the hypothesis suggested above.

We do not know with any accuracy the course of the reaction taken to form the photosensitive substance from its precursor. But the reverse reaction-the formation of precursor from sensitive material—has already been shown to follow the Roscoe-Bunsen rule. Consequently, the quantity of precursor present depends upon the amount of light energy which the animal has recently received.

If a dark adapted Ciona is repeatedly exposed to light at sufficiently close intervals of time, only a negligible quantity of new photosensitive material should be formed. The amount of precursor produced by the light, however, will depend entirely upon the total exposure time. Moreover, if it is true that, in order to act as a stimulus, the amount of precursor formed must bear a constant ratio to the amount already present, the reaction time should always bear the same relation to the reaction times that have preceded it.

This is indeed found to be the case. Cionas that have been kept in the dark for several hours, and are then exposed to light at intervals of minute, and their reaction times taken, follow exactly the prediction outlined above. A curve drawn with time as ordinates, and sensitization periods (reaction time minus 1.76 seconds) as abscissas, has a simple logarithmic form corresponding to the usual Weber-Fechner expectation. If instead, the logarithms of the sensitization periods are used as abscissas, the resulting curve is a straight line. This indicates that the amount of energy required to produce a reaction at any stage in the repeated stimulation is a con

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