his professorship in Johns Hopkins to become director of the new institution. During 1917 steady progress was made in campaigns against hookworm, malaria and yellow fever, in promoting better health administration, in securing reform in sanitary legislation, in persuading governments to increase their expenditure for preventive medicine, and in encouraging public health education. In China the foundation is promoting modern medical education and hospital administration. In September last the Chinese Minister of Education laid the corner stone of the Peking Union Medical College, which is being built in the Chinese capital. The program also includes a medical school and hospital at Shanghai, but the war has interrupted the prosecution of this scheme. The growth of the Rockefeller Institute for Medical Research has called for increasing sums for equipment and current expenses, and £400,000 was appropriated during 1917 as an addition to its endowment.-British Medical Journal.

SCIENTIFIC BOOKS

Fresh-water Biology. By HENRY BALDWIN WARD and GEORGE CHANDLER WHIPPLE, with the collaboration of a staff of specialists. New York, John Wiley & Sons. 1918. 8vo. 1111 pp., 1547 figures in text.

At last American students of fresh-water life are provided with a handbook and guide that will enable them to acquaint themselves with the forms of life found in their native lakes, ponds and streams. Ward and Whipple are the editors, and they themselves contribute five of the thirty-one chapters. Ward writes the general introduction and two chapters on parasitic worms, and one on Gasterotricha, and Whipple writes the concluding chapter on Technical and Sanitary Problems. There are two further introductory chapters, one by Shelford on conditions of existence, and an altogether excellent and practical chapter by Reighard on methods of collecting and photographing. The remaining chapters discuss the principal groups of aquatic organisms and are written by well-known American specialists in the several groups. All are prepared with evi

dent care and with due regard for the needs of the general student and all are adequately illustrated.

Three of these chapters are for reading purposes only-the ones on bacteria by Jordan, on the higher plants by Pond and on aquatic vertebrates by Eigenmann. These are excellent summarized statements of the chief biological phenomena of these groups and are most interesting reading.

The volume is much more than a text-book for the remaining groups (to which 26 chapters are devoted): it is a handbook and guide. and a means of identification, and this is its peculiar merit. Each chapter gives, besides an introductory account of the group, an illustrated key, that is adequate for the determination of the forms and that is convenient and workable. No such set of keys has hitherto been available anywhere. The clear and copious illustrations are placed alongside the reading matter relating to them in the text, and are adequate for the interpretation of the characters used.

This book will at once take its place as the most indispensable reference work for students of freshwater biology; and it is likely to hold that place for a long time.

JAMES G. NEEDHAM

Equido of the Oligocene, Miocene and Pliocene of North America. By HENRY FAIRFIELD OSBORN. Memoirs of the American Museum of Natural History, Volume II., Part I., issued June 10, 1918.

AN extensive memoir of two hundred and seventeen quarto pages, illustrated by one hundred and seventy-three figures, and fiftyfour plates reviews our knowledge, from a systematic standpoint, of the "Equidae of the Oligocene, Miocene and Pliocene of North America."

The present revision of the fossil horses "is iconographic in the sense that all the original type figures of authors are reproduced in facsimile, and all unfigured types, especially those of Marsh, are now figured for the first time. . . ." The work is based largely on the collections at Yale and at the American Mu

seum of Natural History, but a use was also made of type material in other collections.

Osborn's idea in presenting the matter in this form is that "the permanent data of systematic paleontology are the type specimens, determinate or indeterminate, the type locality, the type geologic level. Descriptions, figures, opinions, inferences, phylogenetic and other speculations are subject always to the fallibility of human observation and interpretation." These ideas of course are fundamental and apply to other phases of paleontology than the systematic portion.

A full discussion of the "Genesis and Evolution of Single Dental Characters" is given with abundant illustrations. This is followed by a review of "Geologic Horizons and Life Zones" appropriately illustrated with maps and tables.

The systematic portion discusses one hundred and forty-six species distributed among ten genera. Each species is carefully discussed and the type material illustrated. On turning the pages one is struck by the fragmentary nature of many of the species-but this is the condition throughout all fossil vertebrate groups. To some of the species more information has been added since their description but many of them stand to-day as they were originally described. Many species are known from very complete material.

The contribution is one of which American paleontologists may well be proud. Its permanent character is the careful collection and assembling of data on all species of fossil horses known from the Oligocene to the Pliocene of North America. The magnitude of the task is almost appalling in the amount of detailed work involved. The author tells us that this is a portion of the work done in connection with his "Monograph of the Equide" on which he has been working for the last eighteen years. A portion of the present work is due to the collaboration of Dr. W. D. Matthew to whom the author gives full credit.

The high standard assumed by the publications of the American Museum of Natural History twenty-five years ago is maintained

in the present memoir. The typography and illustrations are excellent. ROY L. MOODIE COLLEGE OF MEDICINE,

UNIVERSITY OF ILLINOIS

SPECIAL ARTICLES

NOTE ON MEASURING THE RELATIVE RATES OF LIFE PROCESSES

THE development of quantitative methods in biology depends largely on finding means of measuring the speed of life processes. In most cases the absolute rate is of less importance than the relative rate (e. g., the normal velocity compared with that observed under the influence of a reagent). Examination of the literature shows that the determination of relative rates is frequently made in a faulty manner, which could easily be avoided by a slight change of method.

We may illustrate this by supposing that the life process in question is a chemical one. The rate of a chemical reaction is expressed by its velocity constant. The simplest case is that in which a single substance, A, decomposes. The usual equation is1

in which K is the velocity constant, T is time and A-X is the amount remaining at any given time, T.

When the reaction is half completed the value of A÷ (A-X) is always 2, no matter what the original concentration of A. The time required to reach this stage of the reaction is inversely proportional to the value of K: for it is evident that if we double the value of K we must halve the value of T, provided the value of A÷(A-X) remains 2, or any other constant value. Hence we see that no matter what stage of the reaction we choose (half completed, one fourth completed, etc.) the velocity constants are inversely pro

1 Natural logarithms give the true value of k, but common logarithms are frequently used: these multiply the value of k by .4343. For illustrations of the application of this equation to life processes see Osterhout, W. J. V., SCIENCE, N. S., 39: 544, 1914; Jour. of Biol. Chem., 21: 585, 1917; Proc. Nat. Acad. Sciences, 4: 85, 1918.

portional to the times required to bring the reacton to the same stage.

This holds not only for reactions of the first order (where a single substance decomposes) but for reactions of higher orders (where two or more substances combine) as well as for consecutive reactions and autocatalysis.

It follows that when a chemical process proceeds at different rates under different conditions, we can compare the velocity constants by simply taking the reciprocals of the times required to bring the reaction to the same stage. If we merely wish to know the relative rates (as is usually the case in biology) it is not necessary to determine the velocity constants at all.

Whenever the initial conditions are the same with respect to concentration we need only compare the times required for equal amounts of work, since these bring the reaction to the same stage.

If on the other hand one attempts to arrive at the relative rate by comparing the amounts of work performed in equal times (as is frequently done in biological research) he can easily fall into serious error. This is evident from Fig. 1, which shows the curves of a reaction proceeding at two different rates, the velocity constant of B being twice as great as that of A. It is evident that the abscissa of A at any point is just twice that of B while no such relation obtains among the ordinates.1 For example at the point C the ordinate of B is twice as great as that of A, while at the point D it is only 1.1 times that of B. Hence it is evident that we should compare abscissæ rather than ordinates (i. e., times required to

2 The principle holds for consecutive reactions in case all the constants are multiplied by the same factor, otherwise not. Cf. Osterhout, W. J. V., Jour. Biol. Chem., 32: 23, 1917

3 Cf. Mellor, J. W., "Chemical Statics and Dy. namics," p. 291, 1909.

4 We can not avoid the difficulty by comparing the rates of the two processes at a given time; for the rates so obtained will bear no constant ratio to each other. Only when they are compared at the same stage of the reaction will they show a constant relation; this gives the relation between the velocity constants.

FIG. 1. Curves showing the same process proceeding at different rates one of which, B, is twice as rapid as the other, A.

experimentation in which, for various reasons, a single observation at one rate is compared with a single observation at another rate. The principle in question is then easily overlooked. In some cases this leads to serious errors.

If we wish to compare the normal rate of a biological process with an abnormal rate (e. g., under the influence of a reagent) it is evident that we can use this principle, but the method of application will depend on circumstances. The normal rate may be constant and its graph a straight line. If this is also true of the abnormal rate it will make no difference whether we compare times or amounts of work.

When the abnormal rate is variable we may have the condition shown in Fig. 2. The normal rate E is constant: the variable abnormal rate F at any point such as H may be determined by drawing the tangent at that point and taking the ratio J÷K.

In many cases it is not possible to secure data for drawing directly such a curve as that shown in Fig. 2. We may, however, deter

perform a given amount of work and take its reciprocal as the rate: this rate is of course an average for the whole period. If the rate is changing during the period the average rate probably occurs near the middle of the period; hence we may place the ordinate representing the rate in the middle of the period as shown in the figure. The resulting curve can be transformed into a curve of the type shown in Fig. 2 by finding the total amount of work performed at any given time: this is accomplished by finding the area enclosed by the curve and the ordinate of the time chosen (since this area is the product of rate by time, it gives the amount of work performed).

Summary.-Measurements of the relative rates of biological processes are frequently made in a faulty manner which may easily be avoided by a slight change of method.

Usually it is preferable to compare the times required to perform a given amount of work (or to bring the reaction to the same stage) rather than to compare the amounts of work performed in a given time.

W. J. V. OSTERHOUT LABORATORY OF PLANT PHYSIOLOGY,

HARVARD UNIVERSITY

TIME

FIG. 3. Curve of a biological process which is studied by measurements of its rate made at frequent intervals. The shaded portions represent periods during which measurements are made. The unshaded portions represent intervals during which there are no measurements.

mine the rate at various periods as shown in Fig. 3, in which the periods during which the rate is measured are shaded while the intervals during which no measurements are made are unshaded.

We can determine the time necessary to

HOW FOOD AND EXERCISE INCREASE
OXIDATION IN THE BODY

LAVOISIER,1 shortly after his discovery that oxygen supported combustion, showed that physical work increased oxidation in the body, thus giving rise to the energy for the work. He also found that the ingestion of food increased oxidation. Rubner2 showed that of the food-stuffs, meat increased oxidation most, fat next, and sugar least. The present investigation was begun in an attempt to find out how physical work and the ingestion of food increase oxidation in the body. We had already found that whatever increased oxidation in the body also stimulated the liver to an increased output of catalase, an enzyme 1 Lavoisier, Mem. de l'Acad. des Sc., 1780. 2 Rubner, "Energiegesetze," 322.

8 Burge, Neill and Ashman, American Journal of Physiology, Vol. XLV., No. 4, pp. 388-395, 500506.

in the tissues possessing the property of liberating oxygen from hydrogen peroxide. Hence the conclusion was drawn that catalase is the enzyme in the body principally responsible for oxidation. Stated more specifically, the present investigation was carried out to determine if the end products of digestion of food, when absorbed from the alimentary tract and carried to the liver, stimulate this organ to an increased output of catalase, which being taken to the muscles and tissues increase oxidation, and if during exercise the liver was also stimulated to an increased output of catalase, thereby increasing oxidation in the muscles and thus furnish the energy for exercise.

The animals used were cats, rabbits and dogs. The catalase in 0.5 c.c. of the blood of the animals was determined by adding this amount of blood to hydrogen peroxide in a bottle at 22° C. and as the oxygen gas was liberated, it was conducted through a rubber tube to an inverted burette previously filled with water. After the volume of gas thus collected in ten minutes had been reduced to standard atmospheric pressure, the resulting volume was taken as a measure of the amount of catalase in the 0.5 c.c. of blood. The material was shaken at a fixed rate of one hundred and eighty double shakes per minute during the determinations. The animals were exercised in a tread-wheel seven feet in diameter and two feet wide. The food materials were carbohydrates (maltose, levulose, dextrose, lactose, honey, cane sugar, cornstarch, dextrin, wheat flour, corn meal, rice flour and fruits (oranges, lemons, apples, bananas, grapebean flour); fats (olive oil, bacon, cream, codliver oil, glycerine, palmitic acid and lard); fruit and rhubarb); proteins (egg, beef, beef extract, beef juice, aminoids and peptone); beverages (coffee, milk, chocolate, tea and cocoa).

The catalase of the blood of the animals was determined before as well as at fixed intervals after the introduction of the food materials. It was found that the ingestion of the simple sugars, dextrose, etc., increased the catalase of the blood very quickly and in some cases as much as 40 per cent. above the normal.

The starchy foods, flour, etc., increased the catalase of the blood, but not so quickly as did the simple sugars. The quicker action of the simple sugars was attributed to the fact that these substances are absorbed immediately and taken to the liver, whereas the starchy foods had to be digested before absorption. Proof that the simple sugars increase the catalase of the blood by stimulating the digestive glands, particularly the liver, to an increased output of catalase, is offered in the following experiment. After etherizing a dog, the abdominal wall was opened and the liver exposed. A comparison was made of the amount of catalase in the blood taken directly from the liver with the amount of blood coming from the tissues, that in the blood of the jugular vein, for example. The blood in the liver or coming directly from the liver was always found to be richer in catalase by 15 to 20 per cent. than the blood taken from any other part of the body. This comparison was made in a great number of animals and is taken to mean that the liver is continually replenishing the catalase of the blood which is being continually used up in the oxidative processes of the tissues. After introducing a simple sugar, such as dextrose, into the etherized animal with its abdominal wall opened, the catalase of the blood taken from the liver was increased much more extensively and rapidly than the blood from a vein such as the jugular. This observation is interpreted to mean that after absorption the sugar was taken to the liver and stimulated this organ to an increased output of catalase. The end products of digestion of the other food-stuffs were tried in a similar manner and all these substances were found to stimulate the liver to an increased output of catalase, meat digest being most effective, fat next, and sugar least.

Of the fats both the olive oil and bacon produced a very quick and pronounced increase in the catalase of the blood, whereas the cream, lard and butter did not act so quickly, due presumably to their slower absorption from the alimentary tract. Coffee, milk, cocoa and tea did not produce an appreciable increase in catalase, while chocolate did. The