public MolecularObject whichMolecularObject(int x, int y) {
		Molecule mol;
		synchronized (molecules.getSynchronizationLock()) {
			for (Iterator i = molecules.iterator(); i.hasNext();) {
				mol = (Molecule) i.next();
				if (mol instanceof MolecularObject) {
					if (((MolecularObject) mol).contains(x, y))
						return (MolecularObject) mol;
				}
			}
		}
		return null;
	}