which the demobilization of medical men may best be carried out is being carefully studied by the British Medical Association. They will no doubt be released gradually as the other branches of the army are demobilized, but many will be eager to return to civil life, and in any estimate of the numbers of the medical profession in this generation regard must be had to the fact that during the last three years practically all newly qualified practitioners have been taken into the army. Within some not very long time after the conclusion of war many of them will be liberated to return to civil life, and will naturally and properly have the first claim upon the public and upon pubic authorities.

Another feature of the last four years has been the great increase in the number of women going in for the study of medicine. In May last there were 2,250 women medical students in the United Kingdom-a figure 23 per cent. greater than the total for January, 1917, and several times larger than in 1914. For this remarkable growth the war must be held mainly responsible. As for the professional instruction of these large numbers of students, men and women alike, there can be no doubt that the war by diverting the activities of many of their teachers into other channels or other spheres has considerably depleted the staffs of the medical schools as well as of other educational institutions in which the preliminary subjects and various branches of medical science are taught. Nevertheless, the teachers who continue at their posts are making every effort to maintain the standard of instruction, in spite of war-time difficulties.

What will be the prospects of the medical profession when the war is over? The medical services have acquitted themselves extremely well in the war, and medical science will come out of it with an enhanced reputation. Military medicine and surgery have advanced, and not a few of the results of practise and research in the war zones will remain as permanent additions to knowledge. The treatment of wounds has steadily improved, orthopedic treatment for the crippled and maimed is more successful than ever; preventive medicine in camp and trenches has

scored great triumphs; the work of the pathological laboratory and of the bacteriologist has proved to be of the utmost value. In civil life the spirit of the times is all in favor of extension and coordination of the public health services. This is reflected in the widely-supported proposal for the setting up of a Ministry of Health, which has received fresh impetus during the past few months. The Minister of Reconstruction, according to rumor, has had a draft bill in his pocket since the beginning of the year, but it does not appear to have won the approval of the Committee of the Cabinet on Home Affairs. The possibilities of the future are large, but as yet ill defined. More medical care has been provided for expectant mothers, for infants, for children, and for the victims of venereal diseases; a great increase in the public work of pathological laboratories all over the kingdom may be confidently expected. All this means an increase in the official medical services. ultimate fate is in store for the private practitioner we will not venture to foretell. Before the war, as we have pointed out above, his position had been profoundly affected by the Insurance scheme which converted the majority of general practitioners into part-time civil servants and subjected them to the discipline of Insurance Commissioners. Pecuniarily it has benefited some and impoverished others. One thing at least can be said: the immediate future is full of uncertainty, especially for the general practitioner. Forces which had long been at work beneath the surface have gained strength through the circumstances of war and many believe that the state will gradually tighten its grip on the medical profession.

What

Every doctor should possess a strong sense of esprit de corps. Medicine is a profession which, when it comes to business dealings of any sort, the general public-as also public authorities-persistently regard as being of a semi-philanthropic character. Furthermore, it is a profession whose aims and requirements are very ill understood by persons who have not undergone a medical education. Hence the interests of the medical profession, both on its financial and scientific sides, are continu

ally being attacked, sometimes openly, sometimes insidiously. It is all-important, therefore, that medical men and women should band themselves together for the common protection of themselves and the profession to which they belong, and to this end join the British Medical Association. For the objects of this body are to promote the progress of medical science and the interests of the medical profession, and its past history shows that it has well fulfilled them.-The British Medical Journal.

SCIENTIFIC BOOKS

The Wings of Insects. By J. H. COMSTOCK. Ithaca, N. Y., The Comstock Publication Company. Pp. xviii+ 423, 9 plates and 427 figs.

In these days of distraction from pure science it is a pleasure to note the appearance of Professor Comstock's book on the wings of insects. The whole book is devoted to an exposition of the uniform terminology of the wing veins of insects, a field of scientific research in which Professor Comstock has long been preeminent. The book is founded upon the now well-known theory that the wing veins of insects can only be homologized by a study of the trachea which precede them, The historical phases of this theory are discussed together with the general features and development of the wings of insects. A general chapter that ought to be appreciated is the one on paleontological data. Professor Comstock's conclusion after reviewing the various fossil forms is: "A study of the paleontological data confirms to a remarkable degree the conclusions drawn from the study of the ontogeny of living insects as to the probable primitive type of wing venation."

Following the general chapters are special chapters devoted to the wings of the various orders of insects. In these chapters the author has not only used the results of his original investigations but has also used the results of various workers who have given special attention to the different groups. These two sources of information have been welded into a concrete whole that taken to

THE PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES

THE fourth number of Volume of the Proceedings of the National Academy of Sciences contains the following articles:

Dynamical aspects of photosynthesis: W. J. V. OSTERHOUT and A. R. C. HAAS, Laboratory of Plant Physiology, Harvard University. Ulva, which has been kept in the dark begins photosynthesis as soon as it is exposed to sunlight. The rate of photosynthesis steadily increases until a constant speed is attained. This may be explained by assuming that sunlight decomposes a substance whose products catalyze photosynthesis or enter directly into the reaction. Quantitative theories are developed to account for the facts.

Mobilities of ions in air, hydrogen and nitrogen: KIA-LOK YEN, Ryerson Physical Laboratory, University of Chicago. Extensive experiments, the rusults of which are in perfect accord with the "small-ion" hypothesis, as contrasted with the "cluster" hypothesis.

Thermo-electric action with dual conduction of electricity: EDWIN H. HALL, Jefferson Physical Laboratory, Harvard University. A continuation of previous papers. The hypothesis of progressive motion by the "free" electrons only has been extended to the case of dual electric conduction.

Terrestrial temperature and atmospheric absorption: C. G. ABBOT, Astrophysical Observatory, Smithsonian Institution. The earth's surface sends out 0.50 calorie per cm2 per minute on the average, and of this only a small part escapes to space. Hence, the atmosphere is the main radiating source, furnishing three fourths of the output of radiation of the earth as a planet.

A contribution to the petrography of the South Sea Islands: J. P. IDDINGS and E. W. MORLEY, Brinklow, Md., and West Hartford, Conn. Thirty detailed chemical analyses of lava from the South Pacific Islands are given, with a discussion of the results.

The law controlling the quantity and rate of regeneration: JACQUES LOEB, Rockefeller Institute for Medical Research, New York. The quantity of regeneration in an isolated piece of an organism is under equal conditions determined by the mass of material necessary for growth circulating in the sap (or blood) of the piece. The mystifying phenomenon of an isolated piece restoring its lost organs thus turns out to be the result of two plain chemical factors, the law of mass action and the production and giving off of inhibitory substances in the growing regions of the organism.

National Research Council: Minutes of the first meeting of the Executive Board of War Organization; Research Information Committee.

THE fifth number of Volume 4 contains the following articles:

Some spectral characteristics of cepheid variables: W. S. ADAMS and A. H. Joy, Mt. Wilson Solar Observatory, Carnegie Institute of Washington. The hydrogen lines are abnormally strong in Cepheid spectra, which are classified first on a basis of the hydrogen lines, and, second, on the more general features of the spectra.

Types of achromatic fringes: CARL BARUS, Department of Physics, Brown University.

Interference of pencils which constitute the remote divergences from a slit: CARL BARUS, Department of Physics, Brown University.

A study of the motions of forty-eight double stars: ERIC DOOLITTLE, Flower Observatory, University of Pennsylvania. A classification of the stars is set up for the purpose of deter

mining those pairs upon which observations are most urgently needed.

The structure of an electromagnetic field: H. BATEMAN, Throop College of Technology, Pasadena. All electrical charges are supposed to travel along rectilinear paths with the velocity of light. When electricity appears to move with a smaller velocity, it is made up of different entities at different times.

Invariants which are functions of parameters of the transformation: OLIVER E. GLENN, Department of Mathematics, University of Pennsylvania. A general discussion of a systematic theory and interpretation of invariantive functions which contain the parameters of the linear transformations which leaves invariant a binary quadratic form, including the invariants of relativity.

THE sixth number of Volume 4 contains the following articles:

Effects of a prolonged reduction in diet on twenty-five men: I. Influence on basal metabolism and nitrogen excretion: FRANCIS G. BENEDICT and PAUL ROTH, Nutrition Laboratory, Carnegie Institution of Washington, Boston. II., Bearing on neuro-muscular processes and mental condition: WALTER R. MILES, Nutrition Laboratory, Carnegie Institution of Washington, Boston. III., Influence on efficiency during muscular work: H. MONMOUTH SMITH, Nutrition Laboratory, Carnegie Institution of Washington, Boston.

Possible action of the sex-determining mechanism: C. E. MCCLUNG, Zoological Laboratories, University of Pennsylvania.

The study of the sediments as an aid to the earth historian: ELIOT BLACKWELDER, Department of geology, University of Illinois.

The growth of the Alaskan fur seal herd between 1912 and 1917: G. H. PARKER, United States Seal Investigation, 1914. Since 1912 the steady increase in the numbers of pups born, and of harem bulls and the decrease since 1913 of the average harem are most favorable signs in the growth of the herd. The one unfavorable feature during this period is the considerable increase in idle bulls in 1915, 1916 and especially in 1917. This in

crease, which can be eventually checked, shows that active commercial killing should have been restored some years ago.

The destruction of tetanus antitoxin by chemical agents: W. N. BERG and R. A. KELSER, Pathological Division, Bureau of Animal Industry, Washington. The results indicate that tetanus antitoxin a substance of non-protein nature, but the stability of the antitoxin is so dependent upon that of the protein to which it is attached, that whenever the protein molecule is split, the antitoxin splits with it.

Tests for fluorine and tin in meteorites with notes on maskelynite and the effect of dry heat on meteoric stones: GEORGE P. MERRILL, Department of Geology, United States National Museum, Washington.

Notes on isotopic lead: FRANK WIGGLESWORTH CLARKE, United States Geological Survey, Washington. Investigations on the atomic weight of various forms of lead, and radioactive estimates of the age of minerals, are analysed for the purpose of throwing light upon isotopes and the structure of chemical elements.

THE seventh number of Volume 4 contains the following articles:

On the representation of a number as the sum of any number of squares, and in particular of five or seven: G. H. HARDY, Trinity College, Cambridge, England.

The crystal structure of ice: ANCEL ST. JOHN, Department of Physics, Lake Forest College. Ice is properly assigned to the hexagonal system, and consists of four interpenetrating triangular lattices, of which the fundamental spacings have been obtained.

Fringing reefs of the Philippine Islands: W. M. DAVIS, Department of Geology and Geography, Harvard University. An interpretation of recently published large-scale charts of the United States Coast and Geodetic Survey.

Dilation of the great arteries distal to partially occluding bands: WILLIAM S. HALSTEAD, Medical School, Johns Hopkins Uni

versity. The relative amount of constriction required to give the most pronounced results has been determined, so that the author is able, in almost every instance, to produce the dilation, and a large amount of material thereby accumulated is analyzed.

On the correction of optical surfaces: A. A. MICHELSON, Ryerson Physical Laboratory, University of Chicago.

EDWIN BIDWELL WILSON MASS. INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASS.

SPECIAL ARTICLES

INVESTIGATIONS ON THE IMBIBITION OF WATER BY GELATINE

MANY investigators in both botany and zoology have recently been at work on the absorption of water by gelatine and other colloidal jellies and from their results have drawn some extremely interesting conclusions However as regarding physiological behavior. the published results accumulate many apparent discrepancies in actual experimental results are appearing. In an attempt to investigate some phases of imbibition by gelatine, I found difficulty in making my conclusions agree with those of previous workers and even in duplicating my own results. In the course of this work certain phenomena of the behavior of gelatine itself came to light and I am offering the following account of some of the preliminary work which I found necessary, in the hope that it may save other workers needless trouble and perhaps help to clear up some of the discrepancies referred to.

Various authors have emphasized the necessity for using material of a constant chemical composition, and for conducting all comparable tests at the same temperature, but the importance of an identical history of watercontent and of water-loss seems to have been overlooked.

As was to be expected, the water-content of the gelatine at the beginning of the absorption, strongly influences the rate of water uptake. However, even when different lots of gelatine have the same water-content at the beginning of the absorption, their ability to

absorb water still depends upon their respective water-contents when they were made up, as Table I. shows. Several lots were made up to the concentrations given in, the heading of the table, poured out on glass slabs, and allowed to lose water by evaporation at room temperature until tests showed that all had attained the same water-content (one gram gelatine.to 0.17 grams water). Then pieces of the same size and form were placed in distilled water and their increase in thickness measured at intervals. The table shows that the lot which had the highest original percentage of water, increased in size most rapidly. That this meant a real difference in the amount of water absorbed was shown by the tests of the water-content at several stages. After 136 hours the pieces which were originally made up to contain 11 per cent. gelatine, had a water content of 98.4 grams per gram of gelatine. At the close of 160 hours the original 20 per cent. gelatine contained 178.0 grams of water per gram of gelatine, and the 33 per cent. gelatine, 100.0 grams of water per gram of gelatine.

The above results indicate that the evaporation of water from the gelatine influences any subsequent absorbing rate. The evaporational history of the gelatine used affects also the distribution of the increase in size among the several dimensions of any given piece, as is shown by the following conclusions which have been drawn from a large number of experiments. The tables to which reference is made contain fair samples of the many readings taken. The tests were made upon gelatine of several concentrations varying from 10 per cent. to 33 per cent. The pieces referred to were rectangular blocks 2.00 X 0.35 X 0.35 cm.

1. When no appreciable amount of water has evaporated from the gelatine since it has set, blocks swell equally in length, thickness and breadth. This is true whether five minutes or forty-eight hours has elapsed since the setting. See Table II.

2. These blocks, when placed on a glass plate with their largest faces in a horizontal position, and allowed to lose water by evap

oration at 18° to 30° C., shrink about twice as much in the two short dimensions as in the long one, shrinking being calculated as percentage of original size. See Table II.

3. When the blocks which had received the treatment mentioned in paragraph 2 above, were placed in water and allowed to swell the distribution of amount of increase among the three dimensions was in the same ratio that the shrinking had been. That is, the increase in size was about twice as great for the two short dimensions as for the long one. This distribution of increase continued for at least 60 hours after the gelatine had attained its original water-content. See Table II.

4. When blocks were cut from freshly made gelatine and hung on a thread with the long axes in a vertical position, where they were exposed to the air on all sides, the same distribution of decrease in size among the several dimensions took place as was described under paragraphs 2 and 3 above. The subsequent increase in size when blocks were placed in water also showed the same relation as formerly. That is, the shrinking and subsequent swelling were about twice as great in the two short dimensions as in the long one.

5. When gelatine was poured into a large dish or on to a glass slab and allowed to lose water by evaporation before pieces were cut, the decrease in thickness far exceeded the decrease in the other directions and the subsequent swelling in water followed the same proportions. For example, 15 per cent. gelatine when treated in this manner showed swelling to the following amounts: Height, 181 per cent., breadth 15 per cent., length 6 per cent. For the behavior of 33 per cent. gelatine see Table III. The more water lost by evaporation, the greater the difference in the swelling of the heighth and the other dimensions.

The above results indicate that the evaporation of water from the surface of gelatine jelly changes in some way the physical structure of the jelly. There has appeared thus far no evidence to determine whether these changes concern small group of molecules or much larger masses of gelatine. It may be merely that evaporation taking place more