THE EFFECT OF THE WAR ON THE CHIEF FACTORS OF POPULATION CHANGE1

THERE have recently appeared some figures2 regarding the mouvement de la population " in France, Prussia and Bavaria which appear to deserve somewhat more careful analysis than they have received. These figures are derived from official sources and are conveniently collected in the place to which I have made reference.

There are three factors fundamentally concerned in producing changes in the absolute size of the population in a given fixed area (country, province, etc.). These are: 1. The birth-rate,

2. The death-rate,

3. The net immigration rate. Of these factors the two first are, generally speaking, of the greatest biological interest. This is particularly true of such political units as France, Prussia and Bavaria, where in normal times net immigration makes по significant contribution to the population. Under war conditions permanent immigration to these units was nil and may therefore be safely neglected in the following discussion. The relation of birth-rate and death-rate changes to population changes is a simple one and may be put this way. If in a given time unit the percentage

100 Deaths Births

has a value less than 100, it means that the births exceed the deaths, and that the population is increasing within the specified time

1 Papers from the department of biometry and Vital statistics, School of Hygiene and Public This Health, Johns Hopkins University, No. 14. paper recently formed the basis of an evening's discussion at the writer's seminar.

2 Jour. Soc. Stat. Paris, Soixantième Année, pp. 356-361, December, 1919.

—-).

From the raw data of births and deaths given in the source referred to above I have calculated the percentage which the deaths

This percentage is based upon returns for the first three fourths of the year only.

-), Prussia (—), Bavaria (----) and Eng

These percentages are shown graphically in Fig. 1, together with straight lines fitted to each, by the method of least squares. The equations to the straight lines, where y denotes death/birth ratio, and x time, are:

France, y 84.0669+21.0285 x. Origin at 1912. (ii) Prussia, y=59.9+17.1 x. Origin at 1913, (iii) Bavaria, y=42.4668+18.0571 x. Origin at 1912. (iv)

England and Wales, y=45.9335 +6.2571 x. Origin at 1912. (v) From this diagram and the data of Table I. we note.

1. In the year prior to the beginning of the war the death-birth ratio of France was at nearly twice as high a level as in any of the other countries dealt with. This fact was of course well known. With a very low birthrate and a death-rate of the same general order of magnitude as that prevailing in other European countries the French death-birth ratio could not be anything but extremely high.

2. In all the countries here dealt with the death-birth ratio in general rises throughout the war period. This means that the proportion of deaths to births increased as long as the war continued. In France it was slightly more than double in 1918 what it was in 1913. The same was in general true of Prussia and Bavaria. These states started from a very different base in 1913, and the relative rise was even greater.

3. In England and Wales, while the deathbirth ratio increased throughout the war period, the rate of this increase was markedly slower than in any of the other countries dealt with.

4. A straight line is not a particularly good fit to the French curve, but it has been used in order to demonstrate more clearly the general trend. In 1915 and 1916 the French percentage rose markedly above the straight line. These were perhaps the years when the forces of war impinged most heavily upon the French.

5. It is noteworthy that despite the epidemic of influenza in 1918, unprecedented in its severity so far as this disease is concerned, none of the curves shows any sharp or marked rise in that year. The curve for England and Wales comes nearest to showing an effect of

the epidemic, but even then the rise in 1918 is not so marked as one might have expected. 6. The straight lines for France, Prussia and Bavaria are nearly parallel, or in other words have slopes of about the same order of magnitude (cf., the values of b which determine the slope in the straight line equations). The slope of the line for England and Wales is very different from that of the other three.

an

These facts raise many interesting points for discussion. The people of Prussia and Bavaria suffered progressive deprivations in respect of food and other comforts of life throughout the war. The sufferings of the French people in these respects were undoubtedly less severe than those of the Germans. All, however, lived for several years on inadequate diet. This fact alone unquestionably contributed to an ever-increasing deathrate, particularly at the two ends of the life cycle. This same dietary factor undoubtedly also played a considerable part in producing the steady fall in the birth-rate. Here, however, the psychological factor also had a large rôle, and this introduces a point of great interest. Psychologically, the civilian French population and the civilian German population were on a different footing. In the one case, until well into 1918, the attitude was that of the potential conqueror, fighting as an invader in the other's territory. In the other case a war of defense against invasion and further destruction of the home land was being fought. Yet the net effect on the vital indices of the population was, as is shown by the essential parallelism of the straight lines, substantially the same in the one case as in the other. In any other game than war the psychological attitude of offender produces far different results from that of defender. Here the essential and out standing fact is that the net biological outcome of the complex interplay of forces resulting from war was almost identically the same in France and Germany.

Another interesting point is that while France started in 1913 with a death-birth ratio 40 per cent higher than that of the German states-she having at that time an

approximate equality of births and deathsnevertheless the biological changes induced by the war, as expressed in this ratio, were the same for the one as for the others. We are evidently dealing here with deep-seated and fundamental phenomena of racial biology. The biological reactions of French and Germans in respect of a most fundamental phenomenon, the death-birth ratio, were essentially the same, though they started from such different pre-war bases.

The case of England is obviously entirely different. Starting from about the same base as the German states England's biological reaction to war was much less pronounced. There are many explanations, such as better food conditions, different race psychology from any of the other belligerents, etc., which might be brought forward. There appears at the moment no way of accurately evaluating any of these possible explanations. We must perforce rest with the setting forth of the facts. It is worth noting, however, that though England's vital index changed less in degree than that of the other countries, its movement was the same in kind.

There are two other points which one would like to have information upon. The first is: What will be the course of these death-birth ratio curves in the years following 1918? Will they come back to the pre-war level, and if so, how soon? For England and Wales alone is it now possible to get an indication on this point. For the year 1919 the relation 100 Deaths had the value 73 per cent. This Births represents a marked drop, though it does not bring the curve back to the pre-war level. The appearance of official statistics which will make possible the further plotting of the curves of Fig. 1 will be awaited with great interest. In the second place, one would like to know what the appearance of the curve for the United States would be. Unfortunately, we have for the Registration Area of births data only for the years 1915, 1916, and 1917 now available. So few years appear inadequate to set against the longer series for the other countries. RAYMOND PEARL

THE JOHNS HOPKINS UNIVERSITY

COLORED PHOTOGRAPHS OF PLANT

DISEASE SPECIMENS

IN the preparation of a handbook of the diseases of vegetables by the U. S. Bureau of Plant Industry for the Food Products Inspection Service of the U. S. Bureau of Markets, it has been found practicable to make colored illustrations by the aid of a firm of commercial photographers.1

The specimens of diseased vegetables were collected by the writers to a large extent in the Chicago markets and freight yards. In addition numerous field excursions were made into the region surrounding Chicago for the purpose of securing specimens. To date, over two hundred illustrations have been completed, a number of which were exhibited at the Baltimore and St. Louis meetings and aroused a very general and real interest on the part of the botanists. So many questions were asked concerning the process by which the illustrations were prepared that the writers are using this means of making the answers as generally known as possible.

A vertical camera was used and the specimens were arranged on a ground-glass background which eliminates shadows. Occasionally a black velvet background was used, and leaves usually were laid on wet blotting paper to prevent curling. In making the exposures, artificial light was seldom used. Most of the subjects have been reproduced in natural size on 8 by 10 inch negatives. The camera was equipped with Cooke Process Lenses, Series 5, of 16 or 18 inches focal length, or with a Goerz Dogmar lens of 12 inches focal length. Color filters, usually the K2 yellow or the green, and occasionally the red, were used in about 75 per cent. of the exposures. About two-thirds of the exposures were made on Seed's Panchromatic plates and the remainder on Polychrome or Standard Orthonon plates. The legends are etched in the gelatin of the negative. The majority of the subjects have been photographed in duplicate to insure against loss of the record by breakage.

Prints are made either on Defender or Kresko printing-out paper or on Defender or 1 Webster Bros., Chicago, Illinois.

Azo developing paper, preferably the latter in each case. The coloring is secured by painting directly upon the dry prints with transparent dyes. The detail of the image is supplied by the lines of the print itself. Water-soluble aniline dyes in the colors yellow, orange, red, brown, blue and royal blue are commonly used. The original plate is colored with the specimens before the artist and, while it has been necessary to supervise closely the color work on this print, a surprising degree of skill and accuracy has been developed by some of the operatives. Since most truck crop disease specimens are highly perishable and change considerably during the time elapsing between exposure of the negative and the completion of prints, even though held in a refrigerator, it has been found advantageous to register the exact colors on some other print of proper color value at the time of exposure, or if possible to collect fresh specimens of a similar character.

Inasmuch as the print is to serve as a background for the color, the kind of paper chosen and the intensity of the image depend upon the color effects desired. For example, the printing-out paper is desirable for most yellows, browns, and reds, while for purples, blacks, and dark greens the developing paper is preferable. However, the printing-out paper serves very well for the majority of greens and has been more extensively used.

After the dyes are mixed and diluted to secure the desired shade, the gelatin surface of the print is prepared for coloring (probably softened and swelled) by wiping with a cloth moistened with alcohol, ammonium hydroxide, or more commonly saliva, and the dye is applied with a brush in rather liberal amounts of which the excess is removed by means of a blotter. The quality of the color is determined by the proportions of the dye mixture and the type of paper used for the print; the intensity of color is determined by the dilution of the dye, the intensity of the photographic image, and the length of time the excess dye is allowed to remain on the print before blotting. In case of error the

color can be removed with ammonium hydroxide. In some instances a very small amount of this substance added to the dye causes the latter to spread and adhere more satisfactorily. Details in white or background color, such as holes in a leaf, can be conserved by coating with a paste or enamel which is insoluble in ordinary solvents and is removed with benzine after the coloring is completed. Details in black, such as the blackened veins in cabbage black rot, can best be shown by the image on Azo paper. After the coloring is completed, the prints are run through a mordant bath to fix the colors. Combinations of acetic acid, formalin, and other mordant reagents constitute this bath, the exact composition of which depends in part upon the colors to be fixed. The gelatin surface must be thoroughly wetted by the solution. The prints are then rinsed in a water bath, placed face downward on squeegee boards, sponged, and passed through rollers to remove the excess water. The prints are mounted while wet on muslin or Japanese paper with a cardboard flap and allowed to dry on the squeegee board.

While these colored photographs are ultimately to be used for lithographs, it has been found feasible to reproduce about ninety sets of fifty duplicates each for immediate use by hand coloring of duplicate prints, the original colored print being used as a guide. However, this process is too laborious and unreliable for large scale production and the colors will not endure indefinite exposure to light. Colored lantern slides of a very gratifying quality have also been made.

This process of color reproduction could well be utilized in other branches of science and there appears to be no reason why it could not be perfected and employed by educational and research institutions. The results of this method of scientific illustration are far superior to uncolored reproductions and are, it is believed, an improvement over other types of color reproduction because of the accuracy of detail afforded by the photographic image. Such illustrations should find wide use in