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43

THE DEVELOPMENTAL EFFICIENCY OF THE

AVIAN EMBRYO

BY

JOSEPH NEEDHAM, M.A.,

PH.D.,

Fellow of Gonville and Caius College, Cambridge.

(From the Biochemical Department, University of Cambridge.)

(Received ist February 1927.)

(With Two Text-figures.)

CONTENTS.

PAGE

Introduction . . . 4 3

( A ) T h e C h a n g e i n t h e " C o e f f i c i e n t d ' U t i l i s a t i o n " o r " P l a s t i c E f f i c i e n c y C o e f f i c i e n t " d u r i n g d e v e l o p m e n t . . . 4 3 ( B ) T h e C h a n g e i n t h e " R e n d e m e n t E n e r g ^ t i q u e " o r " E n e r g e t i c E f f i c i e n c y C o

-e f f i c i -e n t " d u r i n g d -e v -e l o p m -e n t . . . 4 6

S u m m a r y . . . . . . . - S 3

INTRODUCTION.

IN the consideration of embryonic metabolism it is natural to enquire what degree of wastefulness in growth is shown by the developing embryo. Up to the present time this question has only been answered by treating the ontogenetic period as a whole. The efficiency of growth may vary, however, during that period and a knowledge of the variations in this factor with time might throw some light on the chemical events of incubation. The calculations of this paper were made with this end in view. They were possible because of the general balance-sheet of chemical changes in the developing chick which Murray (16-20) and I myself (31-36) have built up.

(A) THE CHANGE IN THE "COEFFICIENT D'UTILISATION" OR "PLASTIC EFFICIENCY COEFFICIENT" DURING DEVELOPMENT. The degree of efficiency with which the transference of yolk and albumen into flesh and blood is effected may most conveniently be expressed by an efficiency coefficient.

The efficiency coefficient as such corresponds to the " Coefficient d'Utilisation " of Terroine and Wurmser(33), the "Coefficient ficonomique" of Pfeffer(27), and the "Plastic Equivalent" of Waterman(37). The best name for it would seem to be "Plastic Efficiency Coefficient" (P.E.C. for short) for this shows that it has nothing to do with energy content or expenditure and explains that it is a measure of efficiency of transfer of matter. It may be described as the ratio

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[image:2.451.43.411.144.408.2]

and is designed to show the relationship between the substance combusted and the substance stored, or in other words, the relative cost in gm. of solid of building the embryo. The higher the efficiency coefficient, the smaller the amount of burnt substance in relation to stored substance.

Table I. Efficiency Coefficient.

I Day o i 2 3 4 5 6 7 8 9 10 II 12 13 ' 4 15 16 17 18 19 20 2 Cumulative Efficiency Coefficient (Gray) •67 •64 •62

• 6 1 •60 •63

•69

•73

•74

3 4 5

Increments Storage of dry weight mg. 3 7 12 19-4 30-8 44'3 68-2 1025 1607 241-0 409-4 575 686 73° 797 832 Combustion mg. 1 3 6 11 20 32 45 60 80 i°5 132 164 198 236 253 259 Total mg. 4 10 18 3O 5i 76 " 3 162 241 346 541 739 884 966 1050 1091 6 Daily Plastic (incremental) Efficiency Coefficient •75 •70 -67 •69 •60 •58 •60 •63 •67 •69 •75 •77 •77 •76 •76 •76 7 Percentage Plastic Efficiency Coefficient 33 43 50 57 65 66 59 50 44 32 28 28 32 31 31

Gray do) in his recent memoir on the chemical embryology of the trout finds that its average Plastic Efficiency Coefficient (P.E.C.) is -63 which compares very closely with that of the frog, the chick, the silkworm, and Aspergillus. He worked it out for the chick from Murray's data(18) in a cumulative way, but a more in-stantaneous picture would be given if it were calculated on a daily basis. How expensive is it on each day of development to build what is built on that day? Table I, column 1 gives the day and column 2 the P.E.C. as given by Gray. This would not be appreciably different if it were computed using Murray's figures for oxygen consumption (ao) instead of those for carbon dioxide production, as could now be done.

Column 6 gives the P.E.C. worked out for each day, the incremental P.E.C, and in Fig. 1 it is compared with Gray's. Both curves fall and then rise, and the lag in the cumulative one is not significant for each day's point bears, as it were, in itself the effects of the previous days. The incremental P.E.C. shows the instan-taneous change.

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The Developmental Efficiency of the Avian Embryo 45

amount of stored substance then than at any other time. This calls to mind the correlation suggested in a previous paper (23) between heat-production and mid-development, in which it appeared that both for the chick and the toad (Gaydaw) it is most expensive to double the weight of the animal when embryogenesis is half completed. In the chick this is between the seventh and twelfth days. This might be related to the fact that the growth-rate of dry solid is constant during that period, but the fit is not exact for the constancy is hardly established by the seventh day and continues till the fifteenth. There is, moreover, no reason to suppose that an increase of dry substance rather than water should necessarily lead to an increase of catabolism. But the correlation of the intensity of protein combustion is much more exact, in fact, strikingly so, as may be seen from the vertical line in Fig. 1,

•to •

•ss

Days 5- 10 rr

[image:3.451.122.323.231.431.2]

O Gray: cumulative. © Needham: incremental.

Fig. 1. Plastic efficiency coefficient. The vertical dotted line indicates the point of maximum intensity of protein combustion.

and the inference that we have here to deal with an effect of Specific Dynamic Action is difficult to resist. Another explanation is also available. It is just at this period that the transference of fat into protein is probably going on, and, as Terroine, Trautman, and Bonnet (35) have shown, such a transference results in an extra energy-loss of 23 per cent. This might lead to an increased expenditure of substance in a given amount of architectural enterprise. Probably more than one factor is responsible.

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percentage P.E.C, is given in column 7 of Table I. It gives a peak at 8-5 days of development instead of a trough. There can be no doubt of the phenomenon of maximum inefficiency in the middle of the ontogenesis of the chick.

We have seen that the average P.E.C. for the whole of development is -68. It is interesting to enquire which of the foodstuffs contributes principally to this degree of efficiency. Knowing already that fat is the chief foodstuff combusted and that protein is the chief architectural material, it would be natural to predict that the most efficiently stored substance would be protein. The exact figures follow.

Carbohydrate stored burnt Protein stored

burnt Fat stored

burnt

Total solid stored Dry weight of embryo at

195 days app.

mg.

107

2986 69

1700 2110

4793

5000

Reference

(26) Tab. I, col. 5 (26) „ VIII, „ 3 25) „ III, „ 2 (23) „ V, „ 9 (25) „ VIII, „ 3 (25) „ IX, „ 3

P.E.C.

) *

( -98

I

-% of total foodstuff combusted

5-6

302

91-4

Out of 100 gm. of protein in its diet, then, the embryo can store away 98, out of 100 gm. of carbohydrate 82, but out of 100 gm. of fat only 43. This could not have been predicted from the combustion curves alone, but needed a consideration of the constitution of the embryo. The embryo has to thank protein absorption for its average P.E.C. level, and to a lesser degree that of carbohydrate. In the case of animals such as the trout which burn large amounts of protein, the "foodstuff P.E.C." would be very different.

(B) THE CHANGE IN THE "RENDEMENT ENERGfiTIQUE" OR "ENERGETIC EFFICIENCY COEFFICIENT" DURING DEVELOPMENT.

The P.E.C. or Plastic Efficiency Coefficient is based on analyses of actual material. Terroine and Wurmser(33) in their classical paper on Growth Energy have argued, following Tangl(32), that a better idea of the fundamental nature of growth and especially embryonic growth can be got by dealing in energy rather than matter. They therefore define the "Rendement Energ6tique" analogously to the Plastic Efficiency Coefficient as

Energy laid up in the organism

Energy in the raw materials _ Energy in the raw materials at at zero hour the end of development

U'

U-U

B

which is only another way of writing Energy stored

or Energy stored

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The Developmental Efficiency of the Avian Embryo 47

This can be calculated from the results obtained by the following investigators and works out thus:

Tangl(32) chick ... ... ... 66 per cent. Farkas(s) silkworm ... 87 ,, Glaser(s) minnow ... ... ... 78 ,, Faure-Fremiet and Vivier du Streel(6) frog ... 82 ,, Barthelemy and Bonnetd) frog ... ... ... 75 „

They proceed to point out, however, that this "Rendement Energ^tique b r u t " contains a fallacy and that to get the "Rendement Energ^tique r^el" the basal metabolism must be taken into account. Tangl's " Entwicklungsarbeit" (Ea) fails to allow for the fact that all the time the embryo is growing it is also eating and every cell as soon as formed begins a normal metabolic life; it is thus only a measure of the total embryonic metabolism. In just the same way the "Rendement Ener-getique brut" fails to allow for the fact that some of the energy absorbed by the embryo is expended in basal metabolism, maintenance energy, "energie d'entre-tien," etc. to which the embryo is committed by the mere circumstance of being alive at all. Thus of the energy in the material combusted only a certain fraction ought really to be included in the calculation of the efficiency, for the rest is ear-marked for the upkeep of that part of the building already constructed and cannot be termed in any sense a waste. The " Rendement Energetique brut" does not take into account the fact that every cell embarks upon a basal metabolism as soon as it is completed. A calculation of the true growth energy must therefore allow for-this according to the following formula:

Energy laid up in the organism U' Energy in the raw Energy in the raw Enerev of u ~ (UR+ UF)

materials at zero - materials at the end + M a i n t~a n c e

hour or development

The denominator is now the energy absorbed for growth and non-basal metabolism only. The strict correspondence between observed and calculated heat-production found by Bohr and Hasselbalch(i) suggests that the energy not allotted to one or other of the above headings will be very small. There is, however, some doubt whether the usual notions of basal metabolism can be applied to so rapidly changing a system as the embryo. Basal metabolism is that amount of energy used in main-taining a steady state, but can the embryo be considered to be in a steady state even momentarily? Perhaps the conceptions of Terroine and Wurmser are not applicable to the cells of a developing metazoon though they may be quite satis-factory for moulds and bacteria.

Terroine and Wurmser (33) not wishing to place confidence in the law of surfaces, especially as applied to Aspergillns niger, determined their UB or basal metabolism

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unfortunately be necessary to have recourse to the law of surfaces using Meeh's formula(15) and Rubner's constant(J8). The calculation can evidently not be exact because we do not know how these quantities vary during the embryogeny of the chick, but it is worth while to probe the matter and see what happens. The relevant figures are shown in Tables II and I I I .

Table II. I Day 0 1 2 3 4 6 8 9 10 11 12 13 14 15 16

\l

19 20 Total 2 3

Surface of the embryo

Total sq. mm. 1005 198 380 586 §47 1170 1550 2000 2510 3080 375° 4490 5290 6150 7130 8170 9280 10700 Daily increments 98-5 182 206 261 323 380 45° 510 570 670 740 800 860 980 1040 1110 1420 i°599 4 gm. cals. produced in basal metabolism daily increments 92 172 194 246 305 35§ 424 481 537 632 698 754 811 924 981 1050 1350 5 6 Calories evolved (Bohr and Hasselbalch)

gm. cals output per day Heat absorbed 1

i!

" 5 151 200 276 396 552 780 IOOI 1240 1460 1710 i960 2160 Daily increments 24 36 31 36 49 76 120 156 228 221 239 220 250 250 200

In Table II, column 1 gives the day of development, and column 2 the calcu-lated surface of the embryo, obtained according to the formula

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calcu-lated value assumes fat only to be burnt would not entirely account for this. Returning to Table II, however, it can at once be seen that the basal metabolism in column 4 invariably exceeds the total amount of heat put out as given in column 6 which is the incrementation of column 5. Thus there is not enough heat put out to account for the amount that ought to be produced in maintenance energy alone. However, there cannot be much doubt that the basal metabolism as here calculated is absurdly high, for if all the increments are added up the result is 61,000 calories, in other words, about four times as much as the total energy known to be lost by combustion. We must therefore suppose either that the surface formula does not hold in embryonic life or that the high temperature (370) in which development proceeds leads to a lower basal metabolism than would be expected. Lusk(i4,.p. 141) says that the minimum requirement for energy is seen to be present when the fasting organism is surrounded by an atmosphere having a temperature of 30° to 350. Most important of all, however, is the probability that Rubner's constant for the hen does not hold for the embryonic chick. It is quiescent, its muscles have no tonus or very little, its respiratory muscles are inactive, and its heart alone is requiring constantly a supply of energy. Since the metabolism is proportional to the superficial area of the animal, it may well be asked what is happening in an embryo at the minute stage when its percentage growth-rate is 1400 (Schmalhausen (39)). The large surface in proportion to its weight which the very young embryo must have explains the fall in metabolic rate and rate of heat-production which has been brought to light by so many investigators, e.g. Le Breton and Schaeffer(ia), and Shearer (30). Columns 2 and 3 do not begin with nearly such small figures as do columns in which weight is expressed.

Evidently it is not possible at present to calculate the " Rendement Energetique reel" or "Real Energetic Efficiency" (R.E.E.); all that can be done is to calculate the "Rendement Energetique brut" or "Apparent Energetic Efficiency (A.E.E.). This is done in Table III. Column 1 shows the time of development, column 2 the energy stored in the embryo taken from Murray's table and expressed as gm. cals. per gm. dry weight of embryo, column 3 the same expressed as actual calories present in the embryo each day (cumulative). Column 4 shows the incre-ments of calories, in other words the amounts of potential energy stored in the embryonic body each day. In order to check this and to show that the data balance properly column 5 shows the energy present in the extra-embryonic part of the egg as determined with the bomb calorimeter by Tangle). It will be seen that the rest of the egg loses, in addition to combustion losses, 250 gm. cals. between the eighth and the ninth days, while the embryo gains 232; a sufficient agreement. The figure of 34,193 gm. cals. seen at the bottom of column 4 representing the number of cals. contained in the finished embryo agrees sufficiently well with the value given by Tangl of 32,000; the latter was measured directly, the former was obtained by the addition of all the increments.

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The Developmental Efficiency of the Avian Embryo 51

this as actual number of mg. burnt each day. Column 8 translates this into inter-diurnal averages, so that the amount of substance combusted in producing the corresponding value of column 4 is there shown for the interdiurnal periods. In column 9 this is seen converted into gm. cals., assuming that 100 percent, instead of the true 92 per cent, of the total solid burnt is fat, and that 1 gm. of fat produces on its combustion 9300 gm. cals. The total of this column amounts to 1700 gm. cals., not very far from the 1650 gm. cals., the Ea of Tangl. In column 10 Tangl's values for column 9 are given, and it may be noticed that they are very close to the newer ones. An error exists here owing to the fact that no account has been taken of the energy left behind in incompletely combusted materials, but as the chief of these is uric acid, and—using the data of Stohmann and Langbein(3O for the calorific value of uric acid, 2750 gm. cals. per gm.—the cals. locked up in this

A.E.E.

6s--60 •

I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I I I I '

S" (o IT 2 o

Fig. 2. Apparent energetic efficiency (Rendement Energe'tique brut).

way only amount to 16 on the nineteenth day or much less than i per cent, of the total combusted, this error is negligible. It may also be noticed, by comparing column 7 with Table I, column 4, that the solid combusted calculated from the carbon dioxide output differs very little from that calculated from the oxygen intake. The variations would perhaps be significant for some purposes but not for the present one. Finally column 11 shows the A.E.E. (" Rendement Energe'tique brut").

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naturally be expected to be very high in the early stages when the embryo is very minute and has a large surface in proportion to its size, one would naturally predict that the efficiency, the A.E.E., would be very low then. Its subsequent rise to a constant level might be associated with the decrease in importance of basal meta-bolism. It is interesting to note that it finishes up very close to the values obtained for the R.E.E., the "Rendement Energdtique r6el," of mammalian post-embryonic growth by Kellner and Kohler(n) and Fingerling, Kohler, and Reinhardt(7). But at the present time there is no means of telling what this latter coefficient would show in the ontogenesis of the chick; it would certainly be much higher than the A.E.E. in the earlier stages but afterwards it might either fall or remain constant. It is difficult to see how the basal metabolism of the embryo could be measured.

Another way of interpreting Fig. 2 would be by the biogenetic law, for the low efficiency of the early stages may not be due to a high basal metabolism then. As a general rule the "lower" the animal the more wasteful it is: Horace Brown, for example (3), showed that a yeast cell would ferment its own weight of maltose at 300 C. in 2-2 hours and at 400 C. in 1-3 hours, during which time it was not repro-ducing and as far as could be seen was not doing any work at all. This metabolic level would be about 100 times as high as that of an adult man. The rise in effi-ciency (A.E.E.) during the development of the chick may perhaps be thought of as a recapitulatory phenomenon.

It may be noted also that if the embryo continued to behave as wastefully all through incubation as it does in the beginning there would not be enough energy in the egg to provide for it: unless the egg were increased to about one and a half times its present size. Even then there would be no reserve yolk at hatching. Is the increase in efficiency due to change of substrate or increasing complexity of embryonic machinery? This is a problem which much future work in chemical embryology will be required to solve. Apparently no conclusions about the sub-stance combusted can be drawn from the A.E.E. For the R.E.E., on the other hand, Terroine, Trautman, Bonnet, and Jacquot(34) have obtained a value of 38 when protein was the principal foodstuff and 58 in the case of sugar. Terroine, Trautman and Bonnet (35) give further a value of 44 for fat. It is true that these figures were all derived from experiments with moulds, Sterigmatocytis nigra and Aspergillus

orhizae, so that it is doubtful whether they can be directly compared with such as

may be found to hold for homoiothermic organisms. If, however, they do form a valid series there, one might predict, bearing in mind the fact that protein, though combusted in greatest amount at the mid-point of incubation, never preponderates absolutely in the solid burnt, that the R.E.E., if it ever becomes possible to plot it, will fall markedly as development proceeds.

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The Developmental Efficiency of the Avian Embryo 53

rapidly, like the metabolic rate. This question can only be answered by the state-ment that the rise in A.E.E. resembles the fall in metabolic rate. It is slow at first and later more rapid. Thus it would seem as if the furious intensity of combustion with which the embryo begins its life was associated with great wastefulness, while later on greater economy would accompany greater frugality. It may be noted that there is no trough on the A.E.E. curve and that it attains an adult value shortly before the end of development. The calorific value of the embryonic tissue also rises during development, and Murray's graph (17, P. 42O shows that it goes up in a curve shaped rather like that for the A.E.E., as in Fig. 2. The two may be related, for the richer in potential energy the embryonic body becomes per unit weight, the more efficient the transfer of energy from the yolk and white might be expected to be. The increasing calorific value of the substance transferred would tend to nullify this tendency but might not abolish it altogether.

Though the curves for P.E.C. and A.E.E. are different, it is interesting to find that the average P.E.C. for all development is -68 while the average A.E.E. is 66 per cent. Out of 100 gm. of solid presented to it, the embryo can store 68; out of 100 gm. calories presented to it, the embryo can store 66.

Finally, the embryo can be compared with other engines. Its business is to store as much energy as is given it with as little loss as possible. The object of the steam-engine is to produce as much mechanical work from the energy given it with as little loss as possible. The efficiency of this process is not great: in the locomotive engine, which is notoriously wasteful, it may not exceed 15 per cent, and Wimperis(38) gives a value of 22 per cent, for the internal combustion engine working on producer-gas. However, a much better comparison is between the embryo and the boiler or the electric battery for these machines do not alter the form of the energy passing through them. According to Low(13), a Lancashire boiler presented with 100 calories in the form of coal only wastes 28: an efficiency of 72 per cent., and, according to Cooper (4), an average electric battery will give back 74 per cent, of the electrical energy put into it. The average A.E.E. of the chick, the silkworm, the minnow, and the frog embryo is 77 per cent, but the R.E.E. would be somewhat higher. It is interesting that the efficiency of the embryo should be of the same order as that of other machines.

SUMMARY.

1. The "Coefficient d'Utilisation" or Plastic Efficiency Coefficient (P.E.C.) has been calculated for each day during development. It has a trough which is deepest between the eighth and ninth days; development is therefore most expensive at this point. The correlation between this and the point of greatest intensity of protein combustion is exact.

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Efficiency cannot at present be calculated for the basal metabolism of the embryo is unknown and it is not certain whether the usual conceptions of basal metabolism can be applied to a rapidly growing and changing organism.

My thanks are due to Professor Sir Frederick G. Hopkins, F.R.S. for his en-couragement and to Miss M. Stephenson, Mr J. T. Mason, Mr H. W. Phear, and Mr J. P. Moyle for various interesting suggestions. I am also indebted to Dr Dorothy Needham for valuable help and to the Government Grant Committee of the Royal Society for a grant towards the cost of these researches.

REFERENCES.

(1) BARTHELEMY and BONNET (1926). Bull. Soc. Chim. Biol. 8, 1071. (2) BOHR and HASSELBALCH (1903). Skand. Arch. f. Physiol. 14, 398. (3) BROWN (1914). Annals ofBotany, 28, 197.

(4) COOPER (1901). Primary Batteries, p. 288. London. (5) FARKAS (1908). Archiv f. d. ges. Physiol. 98, 490.

(6) FAURE-FREMIET and DU STREET, (1921). Bull. Soc. Chim. Biol. 3, 480.

(7) FINGERLING, KOHLER, and REINHARDT (1914). handwirtsch. Versuchst. 84, 149.

(8) GAYDA (1921). Arch, di Fisiol. 19, 211. (9) GLASER (1912). Biochetnische Zeitschr. 44, 180. (10) GRAY (1926). Brit. Journ. Exp. Biol. 4, 215.

(11) KELLNER and KOHLER (1900). Landtoirtsch. Versuchst. 53, 474.

(12) L E BRETON and SCHAEFFER (1923). Travaux de Vlnstitut de Physiol., Faculttde Mid. Strasbourg. (13) Low (1920). Heat Engines, p. 219. London.

(14) LUSK (1919). The Science of Nutrition, 3rd ed. Saunders, Philadelphia, p. 141. (15) MEEH (1879). Zeitschr. f. Biol. 15, 425.

(16) MURRAY (1925). Journ. Gen. Physiol. 9, 1. (17) (1925). Journ. Gen. Physiol. 9, 603. (18) (1926). Journ. Gen. Physiol. 9, 405. (19) (1926). Journ. Gen. Physiol. 9, 789. (20) (1926). Journ. Gen. Physiol. 10, 337. (21) NEEDHAM (1925). Physiol. Reviews, 5, 1. (22) (1926). Brit. Journ. Exp. Biol. 3, 189. (23) (1926). Brit. Journ. Exp. Biol. 4, 114. (24) (1926). Brit. Journ. Exp. Biol. 4, 145. (25) (1927). Brit. Journ. Exp. Biol. 4, 258. (26) (1927). Brit. Journ. Exp. Biol. 5, 6. (27) PFEFFER (1895). Pringsheim's Jahrbuch, 2 7 , 205. (28) RUBNER. Cited in Lusk, as above, p. 119.

(29) SCHMALHAUSEN (1926). Arch. f. Entwicklungsmcch. 108, 322. (30) SHEARER (1922). Proc. Roy. Soc. B, 92, 410.

(31) STOHMANN and LANGBEIN (1891). Journ. f.prikt. Cheni. 44, 380. (32) TANGL (1903). Arch.f. d. ges. Physiol. 9 3 , 327.

(33) TERROIME and WURMSER (1922). Bull. Soc. Chim. Biol. 4, 519.

(34) TERROINE, TRAUTMAN, BONNET, and JACQUOT (1925). Bull. Soc. Clum. Biol. 7, 351.

(35) TERROINE, TRAUTMAN, and BONNET (1926). Ann. Phys. et Phys.-chem. Biol. 2, 172. (36) VOIT (1901). Zeitschr. f. Biol. 4 1 , 120.

(37) WATERMAN (1912). Folia Microbiologica, 4 , 1.

Figure

Table I. Efficiency Coefficient.
Fig. 1. Plastic efficiency coefficient. The vertical dotted line indicates the point ofmaximum intensity of protein combustion.

References

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