Loans from American and French Central Banks of £50,000,000 were insufficient and exhausted in a matter of weeks, due to large gold outflows across the Atlantic. The British benefited from this departure. They could now use monetary policy to stimulate the economy. Australia and New Zealand had already left the standard and Canada quickly followed suit. The interwar partially-backed gold standard was inherently unstable because of the conflict between the expansion of liabilities to foreign central banks and the resulting deterioration in the Bank of England's reserve ratio. France was then attempting to make Paris a world class financial center, and it received large gold flows as well. In May 1931 a run on Austria's largest commercial bank caused it to fail. The run spread to Germany, where the central bank also collapsed. International financial assistance was too late and in July 1931 Germany adopted exchange controls, followed by Austria in October. The Austrian and German experiences, as well as British budgetary and political difficulties, were among the factors that destroyed confidence in sterling, which occurred in mid-July 1931. Runs ensued and the Bank of England lost much of its reserves. Some economic historians, such as Barry Eichengreen, blame the gold standard of the 1920s for prolonging the economic depression which started in 1929 and lasted for about a decade. In the United States, adherence to the gold standard prevented the Federal Reserve from expanding the money supply to stimulate the economy, fund insolvent banks and fund government deficits that could "prime the pump" for an expansion. Once off the gold standard, it became free to engage in such money creation. The gold standard limited the flexibility of the central banks' monetary policy by limiting their ability to expand the money supply. In the US, the central bank was required by the Federal Reserve Act (1913) to have gold backing 40% of its demand notes. Others, including former Federal Reserve Chairman Ben Bernanke and Nobel Prize-winner Milton Friedman, place the blame for the severity and length of the Great Depression at the feet of the Federal Reserve, mostly due to the deliberate tightening of monetary policy even after the end of the gold standard. They blamed the U.S. major economic contraction in 1937 on tightening of monetary policy resulting in higher cost of capital, weaker securities markets, reduced net government contribution to income, the undistributed profits tax and higher labor costs. The money supply peaked in March 1937, with a trough in May 1938. Higher interest rates intensified the deflationary pressure on the dollar and reduced investment in U.S. banks. Commercial banks converted Federal Reserve Notes to gold in 1931, reducing its gold reserves and forcing a corresponding reduction in the amount of currency in circulation.