It is a pleasure to acknowledge the technical assistance of Elizabeth P. McAllan. S-(2-Chloro-4-nitrophenyl)-L-cysteine. This was prepared from 2-chloro-4-nitroaniline by the method of Parke & Williams (1951), when it formed pale-yellow needles from aq. ethanol, m.p. 176-178' (decomp.) (Found: N, 10-15; Cl, 12-45. Calc. for C9H904N2ClS: N, 10-1; Cl, 12-8%). Bray et al. (1959b) report m.p. 1820 for this compound prepared by the method of Suter (1895). Acetylation of the compound with acetic anhydride in 2N-NaOH yielded N-acetyl-S-(2-chloro-4-nitrophenyl)-L-cysteine in cream needles from ethanol, m.p. 1930. Bray, James & Thorpe (1957) report m.p. 192-194°for this derivative.

1. Rat-liver supernatant catalyses the reaction of diethyl maleate with glutathione. 2. Evidence is presented that the enzyme involved is different from the known glutathione-conjugating enzymes, glutathione S-alkyltransferase, S-aryltransferase and S-epoxidetransferase. 3. Rat-liver supernatant catalyses the reaction of a number of other alphabeta-unsaturated compounds, including aldehydes, ketones, lactones, nitriles and nitro compounds, with glutathione: separate enzymes may be responsible for these reactions.

No abstract

€544. A Convenient Solid for Calibration of the Gouy MagneticSusceptibility Apparatus. By B. N. FIGGIS and R. S. NYHOLM. THE measurement of magnetic susceptibilities by the Gouy method is a relative one, the apparatus being calibrated in terms of a substance of known susceptibility, for which water, nickel chloride solution, and powdered cupric sulphate pentahydrate or ferrous ammonium sulphate hexahydrate have been used. The low suceptibility of water is often inconvenient if small tubes are being calibrated. Nickel chloride solution requires accurate analysis before use and ferrous ammonium sulphate is often of questionable purity. This substance and copper sulphate do not pack well and several different values for the susceptibilities of both solids have been reported.The required properties for a calibrant are: (1) Readily available pure;(2) an accurately known and moderate susceptibility (xg = ;(3) stability in moist air;(4) xg must vary in a known and simple way, at least at room temperature; (5) easily and reproducibly packable into the Gouy tube. The complex mercury tetrathiocyanatocobaltate HgCo(CNS), offers some advantages and its susceptibility has therefore been accurately determined. at 20' 1 being used as reference, the gram susceptibility of the complex is 16.44 (-&O.OS) x at 20".As reported elsewhere,l it obeys the Curie-Weiss law, xg cc (T + lO)-l where T is expressed

SENSITIVITY of the bladder epithelium to carcinogenic stimuli was demontrated by the induction of cancer following the introduction of coal tar directly into the bladders of rats (Maisin and Picard, 1924;Picard, 1927). Bonser, Clayson, Jull and Pyrah (1953) showed that the implantation of relatively large paraffin wax pellets without added chemicals into the bladders of rats induced papillomas.On the other hand Rudali, Chalvet and Winternitz (1955) were unable to obtain tumours when small pellets of paraffin wax or cholesterol were inserted into the bladders of rats, but carcinomata were produced with wax or cholesterol pellets containing phenazine, 1: 2-5: 6-dibenzphenazine or 20-methylcholanthrene.The bladders of mice seem to be more resistant to the apparent carcinogenic; action of inert solids than are those of rats so that mice are more suitable animals for the testing of bladder carcinogens.Jull (1951) developed the technique of surgical introduction of wax pellets containing carcinogens into the bladders of mice and this has been used very effectively by Bonser, Clayson and Jull (1951) and by Bonser, Clayson, Jull and Pyrah (1952) in studying the induction of bladder cancer. These authors found that 2-naphthylamine, which induces bladder cancer in dogs and man, does not cause cancer when introduced into the bladders of mice. On the other hand pellets containing 2-amino-l-naphthol, which is a known intermediary metabolite of 2-naphthylamine, produced cancer of the bladder. Thus they showed that the method could give some indication as to whether a carcinogen was acting directly or after metabolic changes. The fact that bladder tumours were obtained with 20-methylcholanthrene and 3: 4-5: 6-dibenzcarbazole suggests that these polycyclic compounds act without undergoing previous metabolic changes.In the present work the technique described by Jull (1951) has been modified in two ways (cf. Boyland and Watson, 1956). Firstly, the substances under test are mixed with four parts of cholesterol and compressed into pellets instead of being mixed with molten wax. Secondly, the opening in the bladder through which the pellet is introduced is tied off with thread instead of being sewn. A disadvantage of this method is that some tumours are induced by cholesterol pellets alone and this must be considered in assessing the carcinogenicity of the substances tested. Bonser, Bradshaw, Clayson and Jull (1956), in a thorough investigation of this technique, obtained tumours in a proportion of mice treated with pellets of paraffin wax. This induction of cancer by chemically inert material is perhaps analogous to the induction of sarcomata by subcutaneous implantation *Present address: Brisban)e General Hospital, Brisbane, Australia.