The difference in quality of milk depends chiefly on the quantity of fat therein: casein, lactose, and mineral matter being nearly constant, water varying but little unless milk is adulterated.

• 奶质量的差异主要取决于它所含脂肪的数量。酪蛋白、糖、物质几乎是稳定的，水有变化但也很小，否则就是奶中掺假。