The transfer of ¹⁴C-creatine to the rat fetus was studied following continuous i.v. infusion into the mother. In the presence of a relatively constant maternal plasma ¹⁴C-creatine concentration, creatine was accumulated by the chorioallantoic placenta and visceral yolk sac to concentrations higher than that found in maternal or fetal plasma. The ability of the extraembryonic membranes to accumulate creatine changed during gestation; nevertheless, these membranes concentrated creatine against a gradient throughout the period studied (14–22 days of gestation). Neither ¹⁴C-creatinine nor ¹⁴C-urea were concentrated in the placentae or fetal plasma when compared to maternal plasma. Simultaneous infusion of β-guanidinopropionic acid with ¹⁴C-creatine reduced both movement and accumulation of creatine into the fetoplacental unit. It is concluded that the accumulation of creatine by the chorioallantoic placenta and by the visceral yolk sac is an active process with creatine diffusing down its concentration gradient into the fetal circulation.

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Carbon black is a finely divided form of carbon produced by incomplete combustion or thermal decomposition of hydrocarbons and used chiefly as a reinforcing filler for both natural and synthetic rubber; other applications are in printing ink, paints and varnishes, plastics, adsorbents, etc. Carbon black represents a typical case of a limited field on which information is recorded throughout a wide variety of sources, varied both in form and subject coverage. Information on carbon black is found throughout the literature of such materials as rubber, petroleum, plastics, paints, inks, and colloids. Information on carbon black manufacture is found mainly in patents.T he point of departure for a literature search on carbon black depends on the investigator. A laboratory chemist, believing that carbon black is some type of soot, may reach for Chemical Abstracts or for one of the rubber trade journals since he knows that carbon black is used in rubber. A literature chemist will turn first to an encyclopedia, hopefully Kirk-Othmer's "Encyclopedia of Chemical Technology." At present it contains the best and most recent general review article on carbon black by W. R. Smith, including a section by D. C. Bean on acetylene black, a related product.Besides encyclopedias the usual sources of general information are textbooks and review articles. Until the recent publication of "Carbon Black Technology-Recent Developments" by R. Powell, there was no "text book" on carbon black. Mantell's "Carbon and Graphite Handbook" contains several pertinent chapters, and Walker's "Chemistry and Physics of Carbon" is another useful source. Several other recent books include chapters on carbon black technology, and a two-volume reference work, "Les Carbones," was published in 1965, in French. A comprehensive, relatively recent review of carbon black technology by Slaniceanu is an excellent source for general background and references to the literature, particularly in conjunction with a separate bibli-515

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