In metabolic balance studies the assessment of the subject's state of balance is derived from estimates of the dietary intake and the excretion in the urine and feces of the constituent under investigation. It Many investigators employ the "time-marker" method for obtaining quantitative fecal collections giving, for instance, two doses of carmine as a marker, collecting the feces passed between the time of appearance in the feces of the first and second doses of marker, and relating this collection to the diet consumled and uirine passed in the interval between the giving of the markers. The success of this method depends upon the clear recognition of the marker in the feces and the accurate collection of all feces passed during the period of study. In investigations in which no marker is employed (i.e., simple "time-collection" studies), accuracy also depends upon the subject's having a regular pattern of colonic emptying.The "inert indicator" method provides an alternative means of estimating the fecal component in balance studies, and it has the big advantage of avoiding the dependence on quantitative fecal collections. It was first used in experiments with animals, and a summarized description of the "Edin indicator method," which used chromium sesquioxide (Cr9O3), was given by Edin, Kihlen and Nordfeldt (1). The theory of the method has been discussed by Stanley and Cheng (2). Various substances have been tried as indicators, but all have to fulfill the following criteria: they should neither be absorbed from nor be chemically altered in the digestive tract (and so be fully recoverable from the feces); they should be nontoxic and should not interefere with the processes of digestion; they should be uniformly dispersed in the feces, after a stufficient time for attainment in the bowel of a steady state with respect to the indicator; and they should be readily estimated quantitatively in feces.Several indicators have been used in a wide range of investigations on different species of animals (e.g., 3-5), but the principal indicators employed in human studies have been Cr.,O3 (1, 2, 6-8) and polyethylene glycol (9, 10). Animal experimiients had shown that Cr2O3 met all the required criteria, and this has been confirmed for man in the above accounts of its application and in our experience. These earlier accounts all had shown that its use in man provided a valid basis on which to express fecal analytical data, when compared wvith "time-collection" studies; one investigation (7) also showed that fecal analyses based on Cr,O3 compared satisfactorily with car-

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The ampulla, isthmus, uterus, and cervix of mixed-age Romney ewes were examined for the presence of spermatozoa 1, 2, 4, 8, 16, 24, 36, and 48 hrs after a single mating. Spermatozoa were recovered from the following sites at the stated intervals after copulation: the cervix 1 hr, the uterus 2 hrs, the isthmus 4 hrs, and the lower ampulla 16 hrs. Peak numbers in all regions occurred 16 hrs after mating. Cervical numbers were noticeably constant up to 16 hrs and then began to fall.Spermatozoa disappeared rapidly from the reproductive tract between 36 and 48 hrs after copulation, probably because of recommencement of normal dioestral flows of luminal fluids.Oxytocin (lI.U.) administered 3t hrs after copulation enhanced the number of spermatozoa reaching the lower ampulla. Synchronisation of oestrus with progesterone appeared to inhibit both the rate of transport of spermatozoa in ewes and the number entering the uterus and isthmus. These findings based on only a small number of animals are discussed in the light of present knowledge on sperm transport in the ewe.

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Development of a marking device for recording oestrous activity of cattle. and particularly suitable for extensive grazing (range) conditions. is described. Its design and operation and testing of marking substances are discussed.