Methods of detection of amphetamine sulfate using surface enhanced Raman scattering (SERS) from colloidal suspensions and vapour deposited films of both silver and gold are compared. Different aggregating agents are required to produce effective SERS from silver and gold colloidal suspensions. Gold colloid and vapour deposited gold films give weaker scattering than the equivalent silver substrates when high concentrations of drug are analysed but they also give lower detection limits, suggesting a smaller surface enhancement but stronger surface adsorption. A 10(-5) mol dm(-3) solution (the final concentration after addition of colloid was 10(-6) mol dm(-3)) of amphetamine sulfate was detected from gold colloid with an RSD of 5.4%. 25 microl of the same solution could be detected on a roughened gold film. The intensities of the spectra varied across the film surface resulting in relatively high RSDs. The precision was improved by averaging the scattering from several points on the surface. An attempt to improve the detection limit and precision by concentrating a suspension of gold colloid and amphetamine sulfate in aluminium wells did not give effective quantitation. Thus, positive identification and semi-quantitative estimation of amphetamine sulfate can be made quickly and easily using SERS from suspended gold colloid with the appropriate aggregating agents.

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IT has already been suggested that most, if not all, methicillin-resistant strains of Staphylococcus aureus have evolved from a single origin (Lacey, 1972a) on the following evidence : that methicillin-resistance is essentially non-transferable ; that, once lost, methicillin-resistance cannot be restored in vitro; and that certain specific genetic markers (penicillinase production, resistance to streptomycin and tetracycline in addition to resistance to methicillin itself) and their location was the same in several strains. But methieillin-resistant strains isolated over the last decade give a variety of phage-typing patterns (Parker and Hewitt, 1970). Furthermore these strains also possess variable patterns of other properties, particularly resistance to erythromycin, neomycin, chloramphenicul, fusidic acid and novobiocin (e.g. Parker and Hewitt). Such variations are not necessarily inconsistent with ihe evolution of the strains from a single source: thus, changes in the lysogenic state (and therefore phage-typing pattern) of staphylococci are In this paper we attempt to strengthen the hypothesis of a single origin for all methidin-resistant strains. We have also characterised some of the genetic elements specifying antibiotic resistance in these strains and considered the way in which the antibiotic resistance has been acquired. MATERJALS AND IWIXODSMethicillin-resistant staphylococci. Strain nos. FAR1 and FAR2 (both isolated in 1971) were supplied by Dr G. A. J. AyliBe, Birmingham, strain no. 8657 was supplied by Dr Elizabeth H. Asheshov, Cross-Infection Reference Laboratory, Colindale, and strain nos. B109 and B262 were isolated in Bristol during 1969 and 1971 respectively. All the cultures had the following characteristics : heterogeneous resistance to methicillin at 37OC, homogeneous resistance at 30% or below and in the presence of 5 per cent. (w/v) NaCl both at W C and at 37OC.Strain nos. 6936 and 649 have been described previously (Lacey, 1972a; and Grinsted and Lacey, 1973a respectively).Various tests md treatments. Media, detection of loss of antibiotic resistance, recording of pigment, bacteriophage typing, mitomycin Ginduction, irradiation of lysates with ultraviolet 0 light and transduction were as described previously (Lacey, 197%).Determination of minimum inhibitory concentration ( M K ) of antibiotic was by incorporating doubling dilution of each antibiotic into nutrient agar. Generally the inoculum consisted ~~

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