Explanation:

- The provision of medical benefits as non-cash benefits was a significant development in Indian labor welfare.

- Option 1: The Employees' State Insurance Act, 1948 - Correct. This Act introduced a comprehensive social security scheme that included medical benefits as a non-cash benefit for the first time in India, covering sickness, maternity, disability, and more.

- Option 2: The Factories Act, 1948 - Primarily regulates working conditions but does not primarily focus on medical benefits as a non-cash benefit.

- Option 3: The Maternity Benefit Act, 1961 - Provides maternity benefits but not as non-cash medical benefits.

- Option 4: The Mines Act, 1952 - Regulates working conditions in mines but does not specifically introduce non-cash medical benefits as the primary focus.