signals dictate preferential synthesis of additional energy-converting machinery, formation of other cell components es- sential for rapid growth [such as ribo- somes (18)] would be inhibited and, inevitably, the growth rate would be decelerated. A regulatory system per- forming in this fashion should be char- acterized as a partially compensatory control mechanism rather than as a finely tuned regulation device. It seems likely that in addition to changes in quantity, changes in composition of energy-converting membranes must oc- cur under different nutritional condi- tions to permit economic use of the energy and material resources available for biosynthesis. It is hoped that poly- myxin and related antibiotics will serve as sensitive reagents for defining such alterations. GARY A. SOJKA ASSUNTA BACCARINI* HOWARD GEST Department of Microbiology, Indiana University, Bloominigton 47401 References and Notes 1. A. L. Tuttle and H. Gest, Proc. Nat. Arad. Sci. U.S. 45, 1261 (1959). 2. G. Cohen-Bazire and W. R. Sistrom, in The Chlorophylls, L. P. Vernon and G. R. Seeley, Eds. (Academic Press, New York, 1966), p. 313. 3. , R. Y. Stanier, J. Cell. Comnp. Phys- iol. 49, 25 (1957); W. R. Sistrom, J. Gen. Microbiol. 28, 607 (1962). 4. G. A. Sojka, G. A. Din, H. Gest, Nature 216, 1021 (1967). 5. G. A. Sojka and H. Gest, Proc. Nat. Acad. Sci. U.S. 61, 1486 (1968). 6. G. Cohen-Bazire and R. Kunisawa, J. Cell Biol. 16, 401 (1963). 7. S. C. Holt and A. G. Marr, J. Bacteriol. 89, 1421 (1965). 8. A. Gorchein, Proc. Roy. Soc. (London) Ser. B 170, 247 (1968). 9. S. P. Gibbs, W. R. Sistrom, P. B. Worden, J. Cell Biol. 26, 395 (1965). 10. J. Schroder and G. Drews, Arch. Mikrobiol. 64, 59 (1968). 11. J. Lascelles, in A dances in Microbial Phys- iology, A. H. Rose and J. F. Wilkinson, Eds. (Academic Press, New York, 1968), vol. 2, p. 1. 12. D. S. Steiner, J. C. Bumham, R. L. Lester, S. F. Conti, Bacteriol. Proc. (1969), p. 140. 13. B. A. Newton, Bacteriol. Rev. 20, 14 (1956); in The Strategy of Chemotherapy, S. T. Cowan and E. Rowatt, Eds. (Cambridge Univ. Press, Cambridge, 1958), p. 62. 14. K. Wahn, G. Lutsch, T. Rockstroh, K. Zapf, Arch. Mikrobiol. 63, 103 (1968); M. Koike, K. lida, T. Matsuo, J. Bacteriol. 97, 448 (1969). 15. J. W. Newton, Biochim. Biophys. Acta 165, 534 (1968). 16. A similar effect of polymyxin on the permea- bility of Pseuidottmonas aerutginosa cells to the dye N-tolyl-a-naphthylamine-8-sulphonic acid has been reported by B. A. Newton [J. Gen. Microbiol. 10, 491 (1954)]. 17. G. H. Warren, J. Gray, J. A. Yurchenco, J. Bacteriol. 74, 788 (1957). 18. G. A. Din and H. Gest, ibid. 97, 1518 (1969). 19. C. H. Fiske and Y. SubbaRow, J. Biol. Chem. 66, 375 (1925). 20. M. Avron, Biochin. Biophys. Acta 40, 257 (1960). 21. Supported by NSF grant GB-7333X. We thank Theresa Young and Susan Ray for ex- pert technical assistance. * NATO fellow, on leave from Institute of Botany, University of Bologna. 17 July 1969 3 OCTOBER 1969 Thermal Radiation in Metabolic Chambers Abstract. Emissivities and ratios of surface areas of metabolic chambers and their contents have been usually ignol ed in studies of the metabolic rates of animals. Failure to take these factors into account can lead to errors in the interpretation of results. A wide variety of containers have been used to measure metabolic heat production and the rates of evaporative water loss of animals. Frequently, such chambers have had smooth metal- lic inner surfaces. Generally, such me- tallic surfaces have high infrared re- flectances and low emissivities (1). The exchange of thermal radiation between the animal and the chamber walls is often not considered. If the chamber walls are highly reflective to infrared radiation, the energy reflected back to the animal from the chamber walls may have a significant effect on the energy balance of the animal (2). The exchange of radiant energy be- tween an animal (or plant) and a closed chamber is determined by the surface temperatures and emissivities of the or- ganism and the container walls, their surface areas, and the percentage of each area that "views" the other (the view factor) (3, 4). An equation that describes the theoretical exchange of radiation between an object and its con- tainer may be derived in at least two ways. In an intuitive derivation one may imagine two infinite parallel planes with a finite surface between them. The infinite planes represent the con- tainer walls and the finite surface rep- 1.0 2-100 590 .75 s0 .70 .60 .50 .50 E CY 40 .30 .25 .20 0 .25 50 J75 1.0 A,/A2 Fig. 1. Ratio of actual net radiant ex- change to maximum possible net exchange as a function of area ratios and container emissivities. Maximum net exchange oc- curs when both surfaces have an emis- sivity of 1.0. All solid lines are computed on the assumption that the animal surface has an emissivity of 1.0. The dashed line is the difference in the solution at e2 = 0.05. if ei = 0.95 instead of 1.0. The difference is even smaller at higher values of E2. resents the organism. We here assume for simplicity that the absorptivity of the animal is perfect, that is, absorptiv- ity is 1. Energy radiated from an ani- mal (designated surface 1) will strike surface 2 (the infinite parallel planes) where a fraction will be absorbed and some will be reflected. The proportion of the reflected energy incident on sur- face 1 will be determined by the view (shape) factor from surface 2 to sur- face I (F.,1) (3). The rest will pass the animal and be absorbed or reflected by the opposite plane. On each pass of re- flected energy, some falls on the ani- mal. The equation describing the trans- fer of radiant energy from surface 1 to surface 2 is El- 2 = a2ElaTi A, + a2[[ps(ejoT14A1) - p2(eoaT14A,)F21] + a2p2[p2(eA,oT,f) -p2(esA loaT14) .F2, a!42[p2(eiA,aT04) - p2(e1AsaT34) F21] F21 + (1) or El 2= ce2esAsrT4[l + p2(1 - F21) + p22(1- F21)2 + p,3(1 - F21)3 . . .1 (2) where a is the absorptivity, e is the emissivity, p is the reflectivity, a is the Stefan-Boltzmann constant, T is the surface temperature in °K, and A is the surface area. Since Eqs. 1 and 2 have the form I + x + x2 + x ...=/(-x) (3) then a2elA ,aoT4 = I -p2(I -F21) (4) In similar fashion the radiant energy transferred from surface 2 to surface 1 is c2xe ,A 2F21oaT24 E- I- p2( 1- F21) Since the net energy transferred by radiation is the difference between Eqs. 4 and 5 and A1F12 = A.F,1, Fl2 = 1, ay = r, and a + p = 1 (5). Equation 6 is similar to Christiansen's equation (6). EQe2 A =a(Ts- T24) I1 + (1/e2 - 1) (A,IA2) (6) where Q12 is the net transfer of energy from surface 1 to surface 2. A more 115 (5)