This change of concentration at a surface, brought about by surface forces, is spoken of as adsorption. We see the effect of adsorption, for example, in the removal of coloring matter from solution by charcoal. By reason of its high adsorbing power, charcoal was employed, during the great war, in the construction of gas masks for the adsorption of so-called poison gases -many of which were not gases at all, but finely subdivided solids-colloidal smokes-similarly, the recently introduced, highly porous silica gel is used for the recovery of volatile solvents, for the removal by preferential adsorption of gasoline from natural gas and for freeing crude petroleum from deleterious sulphur compounds.

In the production and characterization of colloidal systems, adsorption plays a very important part. By the adsorption of ions from the dispersion medium or from electrolytes present in the solution, the colloid particles acquire an electric charge; and adsorption of the dispersion medium as a whole may also take place to a greater or less extent whereby variation in the general behavior of colloids may be produced. In the case of the so-called suspensoid colloids or hydrophobe colloids, such as colloidal solutions of gold, or arsenous sulphide, the dispersed particles may adsorb none or practically none of the dispersion medium and they exist therefore in suspension as non-hydrated particles, the stability of which is due to their electric charge and to their Brownian movement. In the case of the so-called emulsoid or hydrophile colloids, such as solutions of gelatin or starch, the dispersion medium itself is adsorbed and the stability and properties of such a colloidal solution are due to the adsorbed water as well as to the electric charge on the particles; the greater the adsorption of the dispersion medium, the more will the stability and properties of the colloidal solution be dependent on this adsorbed medium and the less will they depend on the electric charge.

If the electric charge on a suspended colloid is neutralized, agglomeration of the particles followed by precipitation takes place, and this neutralization can readily be effected by the addition of electrolyte.

Negatively charged colloid particles will preferentially adsorb the positive ions of the added electrolyte, and positively charged colloids the negative ions, thus neutralizing the charge on the colloid. Although multivalent ions are in general, according to Hardy's rule, more effective in producing precipitation than univalent ions, recent investigation shows that there is no exact relationship between valency and precipitating power, and that the adsorbability of the ion may exercise an important influence. In the precipita

tion of colloidal sulphur, for example, caesium ion is a hundred times more effective than the lithium ion and has a greater precipitating power than the bivalent ions of zinc, cadmium or nickel.

The precipitation of fine particles by electrolytes is well illustrated in nature, where the finely divided clay carried by many rivers is deposited when the river water mingles with the sea, thus silting up river mouths and forming deltas.

The electrical charge on a colloid particle may be neutralized not only by the ion of an electrolyte, but also by another colloid carrying an electric charge of opposite sign. Colloids of opposite sign may mutually precipitate each other and produce adsorption complexes, as Bancroft has called them, which simulate chemical compounds.

Purple of cassius, for example, is an adsorption complex of stannic oxide and colloidal gold.

Although mutual precipitation may take place essentially as a result of adsorption, chemical reaction may later occur. As Bayliss has shown, when alumina adsorbs free congo red acid, which is blue in color, a blue precipitate is formed, but when this precipitate is suspended in water, the blue color changes to red, which is the color of the salts of Congo red.

Adsorption plays an important part in the dyeing of textiles and the staining of animal tissues. Here the negatively charged color ion of the acid dyes is predominantly adsorbed by a positively charged fiber, and a positively charged dye (basic dye) by a negatively charged fiber.

In an acid both the positive charge on the fibers is increased by adsorption of hydrogen ions and adsorption of a negative or acid dye by the fiber is increased. On the other hand, in alkaline solution, the negative charge on the fiber is increased, and adsorption of a positive or basic dye by the fiber is facilitated.

Similarly, addition of a salt giving a readily adsorbed ion, e.g., sulphate ion, will both increase the adsorption of a basic dye and diminish that of an acid dye.

In the case of substantive dyes, the dye itself is in colloidal solution and addition of electrolyte, in small amount, increases the dye adsorption by diminishing the stability of the colloid.

Where mordants are used, adsorption takes place, the mordant, a colloid, adsorbing the dye from the dye bath and fixing it on the fiber. It is really the mordant that is dyed, not the fiber.

After the dye has been adsorbed, secondary changes may take place, leading to the formation of a more stable adsorption complex.

In the face of colloidal solutions of the gelatin type, the stability of the colloid is due mainly to adsorbed water or adsorbed dispersion medium, and consequently such solutions are not so sensitive to added electrolytes. Although the addition of small amounts of an electrolyte may produce changes in the amount of water adsorbed by the colloid, actual precipitation does not take place until the concentration of added electrolyte is relatively large.

The comparatively great insensitiveness to electrolytes, shown by hydrophile colloids of the gelatin type, may be transferred to hydrophobic or suspensoid colloids of the colloidal gold type.

When gelatin, for example, is added to a colloidal gold solution, the gold is adsorbed by the gelatin and a much greater concentration of electrolyte is required in order to precipitate the gold that is necessary in the absence of the gelatin. The gelatin is said to protect the gold. This so-called protective action, which varies greatly in different hydrophile colloids, is of much importance in many directions.

In the Mississippi and Nile rivers the water is always turbid and muddy, owing to the presence of a large amount of colloidal organic matter which stabilizes the fine suspension of clay and soil; and it is only when the rivers reach the salt water of the sea, with its high concentration of salts, that the finely dispersed mud is precipitated, forming deltas.

The water of the Ohio River, on the other hand, is at all times clear, owing to the absence of protective colloids and the presence of lime and other salts which act as precipitating agents.

By the use of protective colloids, sparingly soluble substances produced by chemical reaction can be kept in a colloidal state and so prevented from undergoing flocculation and sedimentation. In the production of the photographic plate, the silver bromide is prevented from forming a precipitate of coarse particles unsuitable for photographic purposes and is kept by the protective action of gelatin in a finely divided form.

In many physiological processes the protective action of hydrophile colloids may also play an important part. In normal bile, the bile salts, albuminoids, etc., act as protective colloids which keep the sparingly soluble substances, such as cholesterol and the calcium salt of bilirubin, in the colloidal state and so prevent their deposition, but when the amount of protective colloids is reduced by pathological conditions, deposition of the sparingly soluble substances, as gall stones, takes place.

The nature of the curd that separates from milk and the readiness with which it is formed are greatly affected by the presence of protective colloids. Cow's

milk contains a large amount of casein and a small amount of the protective colloid, lactalbumin. It, therefore, curdles readily. In human milk there is a smaller proportion of casein and a larger proportion of lactalbumin, so that the casein is more effectively protected and curdling takes place less readily. In asses' milk the relative proportion of protective colloid is highest of all, and curdling takes place with greatest difficulty. The digestibility of asses' milk is consequently greatest. By increasing the amount of protective colloid in cow's milk, by addition of gelatin or white of egg or even of barley water (starch) curdling occurs less readily and the digestibility of the milk is increased.

The smoothness of a good ice cream also is due to protective colloids, such as gelatin or white of egg, which prevent the coagulation of the casein and keep the crystals of ice extremely small.

Many colloids of the hydrophile type, e.g., gelatin, fibrin, etc., when cooled, pass into a jelly, owing to a coalescence of the hydrated colloid particles. This jelly may be dried and is then obtained as a more or less hornlike material, such as ordinary dry gelatin. These jellies have the important property of taking up or imbibing water, even against very great pressures. This imbibing power is of great biological and agricultural importance. The amount of water imbibed is greatly affected by the presence of electrolytes, being increased by acids and alkalies up to a certain concentration, but the increased swelling produced by dilute acids is diminished by the addition of salts.

The protoplasm of the cells, as has been demonstrated by Gaidukov and by Price, consists of a mixture of colloids. In the cell we have a complex emulsion which under the changing conditions of life may vary in consistency from that of a colloidal solution to that of colloidal gel or jelly. In this system there occur processes of adsorption, changes in dispersity and alterations of the distribution of water between the colloidal particles and the dispersion medium. The living protoplasm, indeed, is a complex system of colloids between which the mutual relations are in a constant state of flux under the action of electrolytes and of stimuli of different kinds; and in which the mass law relationships are altered, now in this direction, now in that, enabling the processes of decomposition and of synthesis to take place. Only in such a colloid system is it possible to have the flexibility and adaptability to the varying requirements of what we call life and growth; just as gelatin, fibrin and other colloids can imbibe and hold large quantities of water, so it is possible for the living organism, aided no doubt by osmotic forces and the

presence of membranes of a semi-permeable character, to hold the 80 per cent. of water present in the body tissues and to preserve the turgor necessary for healthy life. Moreover, the many diverse chemical reactions involved in the breaking down of complex foodstuffs into simple substances and the building up again of these simple compounds into the complex proteins of the protoplasm are accomplished in the living body under the catalytic activity of the enzymes, and these are themselves colloids.

The living organism, therefore, is a vast colloidal community, the diverse members of which are held together in common service by surface forces and by the mutual actions and reactions of electrical changes, and in this community the colloidal workers are engaged in carrying out the multifarious and complex chemical operations on which the life and the health of the community depend.

Martin Fischer has emphasized, perhaps over-emphasized, the analogy between the inhibition of water by gelatin and the water absorbing and retaining power of the colloids of the living organism as affected by variations in the concentration of electrolytes and especially of acids. That work is of great interest and importance, but I wish here to refer more especially to the work of Bancroft and of Clowes on emulsions as affording a suggestive explanation of the action of the plasmatic membrane of cells.

One of the most interesting phenomena in connection with the action of electrolytes on living cells is the so-called antagonistic action of ions. The beat of a heart, for example, continuously perfused with a solution of sodium chloride, isotonic with the blood, soon ceases, but the "toxic" action of the sodium ions can be counteracted by the addition of a small amount of a calcium salt. Similarly, as Loeb showed, the marine organism Fundulus dies when placed in a solution of sodium chloride of the same osmotic pressure as sea water, and it dies also in a solution of calcium chloride. In a mixed solution of these two salts, however, containing the salts in the ratio of about fifty molecules of sodium chloride to one molecule of calcium chloride, the organism continues to live. Since, as Straub has shown, the effect of electrolytes is an effect on the cell membrane, it is to the latter effect that we may turn our attention.

The protoplasm of the living cell is surrounded by a membrane or surface layer which allows the passage of certain dissolved substances but prevents the passage of others. Although in some respects this plasmatic membrane is similar to the artificial semi-permeable membrane, like copper ferrocyanide, experiment shows that very important differences exist. The membrane of the living cell, as Nägeli has shown, is self-forming, and it differs also from the inorganic

semi-permeable membranes in that its permeability may vary and that it is adaptable to the varying requirements of an everchanging life process. While the cell is resting, for example, the plasmatic membrane is impermeable to glucose and the amino-acids, but when the cell passes into a state of functional activity, these substances can pass through the membrane.

The permeability of the plasmatic membrane is also variously affected by different ions. Frog's muscle, for example, placed in an isotonic solution of potassium chloride, is permeable to potassium ions. When, however, sodium and calcium salts, which are normally present in blood plasma, are added, the normal impermeability of the muscle cells to potassium is regained. Although the resting muscle cell is impermeable to potassium salts, the active muscle cell is permeable.

The plasmatic or cell membrane is a surface film or layer comparable with the layer of increased concentration which forms at the boundary surface of a solution when the surface tension of the solvent is lowered by the solute (e.g., solutions of peptone). The materials forming the plasmatic membrane must be drawn therefore from the constituents of the cell, more especially lipoids. Various views have been put forward to explain the selective permeability of the cell membrane, in view of the variability of the cell membrane under different conditions, and more especially of the antagonistic action of ions on the permeability, much interest attaches to the work and suggestions of Bancroft and of Clowes.

When water and olive oil, for example, are shaken vigorously together, the oil is broken up into drops. These drops are comparatively large and no permanent emulsion is formed. In order that the droplets of oil may become sufficiently finely divided and a permanent colloidal emulsion obtained, an emulsifying agent must be added to break up the drops and prevent them from coalescing.

Bancroft has shown that a water solution of a sodium soap has a lower surface tension than when the soap is dissolved in oil, and that when a mixture of oil and aqueous soap solution is shaken, an emulsion of oil in water is formed. On the other hand, the surface tension of a solution of a calcium soap in water is greater than in oil, and therefore an emulsion of water in oil is formed. In the first case the water is the continuous phase, while in the second the oil is the continuous phase.

The reversal of an oil-in-water emulsion to a waterin-oil emulsion can be effected by different salts. Alkali salts, for example, favor the formation of oilin-water emulsions, while calcium salts favor the formation of water-in-oil emulsions. Here again we have

the same antagonistic action of ions as in the case of heart muscle. Similarly, blood plasma may be regarded as an emulsion of fibrinogen and other colloids in an aqueous medium, and the blood clot an emulsion of water in fibrin. The production of the latter system is favored by calcium salts, but is retarded by sodium salts.

Clowes has shown that there is a very close resemblance between the effects produced in emulsions of oil and water and those produced in biological systems, and he has made the valuable suggestion that the cell membrane is a system, a colloidal emulsion, of two phases; a watery solution of protein and a lipoid phase. In the resting state of the cell the membrane consists of an emulsion of protein solution in lipoid, the latter being the continuous phase. In this state, therefore, the membrane will be permeable only to the substances that are lipoid-soluble. In the active state of the cell, there is a reversal of the emulsion, and the aqueous phase becomes the continuous one. In this case, substances soluble in water will now be able to pass through. In each instance, however, regarding the emulsion-membrane as a sieve, the membrane will be permeable only to those substances the particles or molecules of which are small enough to pass through the "pores" between the droplets of the dispersed phase.

We can thus regard not only the protoplasmic cell contents but also the surface layer or cell membrane as a colloid system, and by adopting the view, probably not complete in itself, that the cell membrane is a complex emulsion of colloids, the two phases of which are capable of undergoing reversal, we can explain many of the phenomena associated with the action of the cell membrane.

Although we must recognize the essential importance of colloidal matter in connection with the phenomena of life, and matter in the colloidal state is the vehicle of life; although, further, we may interpret much of the behavior of living matter in terms of physics and chemistry, I am of the opinion that we can not explain life itself in terms of physical science. There seems to be no continuity between inanimate colloidal matter and living matter, but there is a distinct and sharp break in the curve of relations. In other words, life is a new factor, a new set of potentialities, introduced into inanimate matter. Life is a new creation.

UNIVERSITY OF ABERDEEN

ALEXANDER FINDLAY

WALTER SCOTT HENDRIXSON

On July 1, Professor Walter Scott Hendrixson was found dead in his summer cottage at Portage Point, near Manistee, Michigan, where he had been tempo

rarily alone. Death had occurred suddenly from hemorrhage in the brain.

Professor Hendrixson was born in Ohio in 1859; was graduated from Union Central College, Meron, Indiana, in 1881; was instructor and later professor of physics and chemistry at Antioch College, 1882–8; assistant and graduate student in chemistry at Harvard 1888-90, receiving the degrees of A.M. in 1889 and Ph.D. in 1903. He came to Grinnell College as professor of chemistry on the Dodge foundation in 1890, and at the time of his death was the senior member of the Grinnell College faculty, yet a most active and aggressive member and a valued adviser in affairs of the college.

During leaves of absence from Grinnell he had spent one year as graduate student at Goettingen and Berlin; one semester as lecturer in chemistry at the University of Illinois; a year as research fellow at Johns Hopkins University. He was a frequent contributor to the Journal of the American Chemical Society; was a member of learned societies; had served as president of the Iowa Academy of Sciences.

As a teacher, Professor Hendrixson was an inspiration to his students, sending many of them on to graduate and professional work in chemistry. As a chemist, the work of his earlier years was with water analyses and in the investigations of artesian waters underlying Iowa, by the United States Geological Survey. In his later years he has been a regular contributor in the development and applications of electrometric methods in chemistry, his last publication bearing date of May 5, 1925.

As a fitting and permanent memorial of a long and distinguished service, Professor H. W. Norris, a colleague of more than thirty years, has proposed the establishment of the Walter Scott Hendrixson Memorial Fund, for the promotion of research in pure science by members of the faculty of Grinnell College; a fund, the income of which is to be used for the promotion of research by paying the actual expenses involved in original investigations. The aptness of this suggestion was immediately recognized and measures promptly taken looking toward securing an endowment of not less than $10,000 for such a memorial.

FRANK F. ALMY

SCIENTIFIC EVENTS

RESEARCH AND INDUSTRY IN GREAT

BRITAIN

THE British Science Guild have published a report, by the Research and Inventions Committee of the Guild, on the present position with regard to the supply of trained scientific research workers, and their utilization in industry.

The committee find according to a report in. the London Times that, comparing the year 1923-24 with the year 1913-14, the number of full-time students in science at the British universities shows an increase of 60 per cent., while the number of bachelor degrees obtained in science has more than trebled. Over the same period, the number of full-time, postgraduate students engaged in scientific research has increased to more than four times the 1913-14 fig

ure.

The Department of Scientific and Industrial Research, the committee observe, have afforded great assistance to research students in training, but, except in one or two instances, the Research Associations of the department do not appear to be very extensively developed.

The funds at the disposal of the department are large, but in view of the sums annually spent on scientific research in the United States, and our general public expenditure, they can not, in the opinion of the committee, be described as adequate to the great needs of our industries. It appears from inquiries that there is considerable unemployment among recently trained scientific research workers, and that this is most serious in the case of research chemists.

The committee conclude that the value of scientific research to industry is now widely recognized; but that the part that industry itself can play in maintaining an adequate supply of research workers, and in promoting or supporting scientific research, is not so well understood. They suggest that the government could offer considerable inducement to commercial firms to support research, by permitting sums devoted to this purpose to be treated as trade expenses for the purpose of assessment for taxation. They consider it imperative that, before more men and women are encouraged to undertake scientific research training, the demand for them should first be assured. The committee do not look to the greater industrial concerns many of which already realize to the full the value of scientific research-to provide a solution of the present difficulty, but rather to the hundreds of smaller firms whose industrial research associations, if fully developed, could utilize many more scientific research workers; to the benefit, the committee submit, not only of each particular industry, but of the industry of the country as a whole.

The committee further suggest an extension of the method adopted by the various research committees and coordinating boards of the Department of Scientific and Industrial Research, and by the Ministry of Agriculture and other Departments; a inquiry with a view to the establishment of an organization on the lines of the "A. D. Little" Laboratories in the United States; and also an extension of the scheme at present in operation in Bristol University, under which an

industrial firm endows for two years a research student who works on a special line of investigation in the laboratories of the university.

In a memorandum appended to the report the committee strongly recommend the formation of a permanent expert advisory committee on industrial inventions, the functions of which would be (1) to examine the claims of inventions and to decide which are of probable industrial value; and (2) to arrange for the semi-large scale, or complete commercial trial, of inventions passed by the committee.

RESULTS OF THE ASIATIC EXPEDITION OF THE AMERICAN MUSEUM

THE American Museum of Natural History has received cables from Roy Chapman Andrews, leader of the museum's third Asiatic expedition, now in Mongolian territory, giving details of the progress of the expedition. Dr. Clark Wissler has made public the following statement:

The results of the third Asiatic expedition prove the presence of early man in Asia and that is no mean achievement. It is certain that when the first try for paleolithic man in central Asia not only returns rich collections, but reveals two widely separated horizons, it is certain that the whole chapter of stone age history is to be read in Asia as well as Europe. This prospect holds out a promise for America, where there has been no clew to the direct relation of prehistoric man to the ancients of the old world.

Having found the implements which are associated with Neanderthal man in prehistoric Europe it can be safely predicted that sooner or later his bones will be found in Mongolia. The recent discovery of a Neanderthal skeleton in Palestine brings this type of fossil man one step nearer to Central Asia.

This discovery by the American Museum of Natural History adds another epoch to the prehistory of man in Asia. Andrews reports that a large collection has been made, sufficient fully to characterize the culture, and that it is parallel to the Azilian of Western Europe.

Azilian is the last of the old stone age cultures and marks the transition to the neolithic, or second great stone age. But the report goes further in stating that the finds promise to be somewhat older than the Azilian of Europe, which would put them back well within the old stone age.

We are also told that some sites examined yielded mouterian stone tools. This is a period in stone age chronology far back of the Azilian, in fact just before the appearance of the more modern types of man in Europe, or in the time of the Neanderthals.

ANNUAL MEETING OF THE AMERICAN

PUBLIC HEALTH ASSOCIATION THE fifty-fourth annual meeting of the American Public Health Association will be held in St. Louis,