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The whole body retention of cobalt during a period of 400 days after injection of CoCl, has been determined for a strain of specific-pathogen-free albino rats. The method used to fit both exponential and power functions to the data and the application of statistical tests which justify the selection of a function with five exponential terms as the best fit are dcscribed. The statistical mcthods used in this paper are presentcd in detail because of their possible application to other studics of a similar nature.Thc amounts of cobalt in 19 tissucs havc been measured at various times and expressed as concentration factors, which were found to be stablc during the period between 10 and 72 days after injection. However, the concentration factor of bone increascd during a period of400 days at thc cxpense of thc concentrations in the soft tissues. The function developed to dcscribc the whole body retention of cobalt is substantially dilfercnt from that selectcd in ICRP Publication 10 and examplcs of the consequences of applying the two functions to the radiation dosimetry of internal contamination by 6oCoCl, are given. The selection of critical organs for radioisotopes of cobalt is also discussed.

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Biometrika Trust is collaborating with JSTOR to digitize, preserve and extend access to Biometrika. SUMMARYIn testing equality of means of two Normal populations Student's t-test is not generally applicable when the variances of the two populations may be unequal and their ratio is unknown. In the present paper several procedures are considered whereby a preliminary test is performed to ascertain whether or not the variances may be regarded as equal. On the basis of the outcome of this preliminary test one proceeds to test for equality of means. The optimal choice of the level of the preliminary test is made on the basis of controlling the size of the combined test in the sense of keeping it close to a pre-assigned level of significance. Tables of size and power are included to indicate the behaviour of the proposed tests.

DESLAURIERS, R., ZOAMI, J., MGCULLOUSH, R. S., and H~ROUX, 0. 1941. Caloric uptake and cold resistance in cold-acclimated rats fed commercial chow or semipurified diet. Can. J. Physiol. Pharmacol. 49,[707][708][709][710][711][712] Sprague-Bawley male rats fed Master Lab cubes (MLC) or a semipurified diet (T4F) were kept for periods of 1-2 weeks at six subsequent temperatures: 28 "C, 22 "C, 6 "C, 0 "C, -10 "C, and -20 "C. Caloric balance, growth, body temperature, and survival were measured. As previously observed under outdoor winter conditions, with constant laboratory conditions T$ diet was still found to be superior to MLC in allowing a greater degree of cold resistance. At temperatures below 0 "C, in spite of a lower gross energy uptake, T4F-fed rats maintained a faster growth and a higher body temperature than MLC-fed rats, which suggests a greater heat conservation in these animals. Failure of MLC-fed rats to raise their gross energy uptake at -10 "C to a higher level than at 0 "C, and death of most of these animals at -28 "C within the first 3 days strongly suggest a physical limitation in the quantity of high bulk RlLC diet which can be consumed every day, hence a limitation in energy uptake increase. The ability of T,F-fed rats, on the other hand, to raise energy uptake in a continuous linear fashion as temperature is reduced, and their capacity to draw on energy reserves and to survive longer at -20 "C reflect greater metabolic potentials in this group than in MI,C rats. DESLAURIERS, R., ZOAMI, J., MCCWLLOUGH, R. S., et HB~owx, 0. 1941. Caloric uptake and cold resistance in cold-acclimated rats fed commercial chow or semipurified diet. Can. J. Physiol. Pharmacol. 49, 707-712.Des rats m3es Sprague-Dawley nourris avec des cubes '"aster Lab" (MLC) ou soumis au rtgirne semi-purifit (TaF) ont ttk maintenus de 1 B 2 semaines B des temptratures substquentes de 28 "C, 6 "C, 22 "C, 0 "C, -10 "C, et -20 "C. L'appsrt calorique, la croissance, la temptrature du corps et la survie ont Ctt mesurCs. Comme on avait dkj8 pu l'observer l'hiver B IYext6rieur, dans des conditions de laboratoire constantes, le rtgime (T4F) s5est encore montrt suptrieur aux cubes (MLC) pour la rtsistance des rats au froid. Pour les temperatures inftrieures B 0 "C, malgrt la quantitk plus faible d'knergie brute utiliste, ou emmagasinte? par le corps, la croissance des rats soumis au rtgime (T4F) a t t t plus rapide et la tempkrature de leur corps plus tlevte que dans le cas des rats nourris aux cubes (MLC) ce qui conduit penser que ces derniers conservent moins bien leur chaleur. Le fait que les rats nourris avec des cubes (MLC) n'ont pas pu augmenter la quantitt d'knergie brute utiliste, ou emmagasinte, pas leur corps B -10 "C par rapport B celIe correspondant B 0 "C et le fait que ces rats sont pour la plupart morts i i -20 "C en moins de 3 jours induisent B penser que ces rats ont deg difficultts pour consommer le volume nkcessaire de cubes (MLC), caracttrists par un grand volume pour une tnergie donnke et, de ce fait, ne peuvent disposer ...