Tax deduction at source requires withholding on taxable portions of payments to non-residents; officer may determine the portion to withhold. Section 195 requires persons responsible for payments to non-residents to deduct tax at source on sums chargeable under the Income-tax Act; if the payer believes the whole payment is not taxable in the recipient's hands, the payer may apply under section 195(2) to the Income-tax Officer for determination of the taxable portion. Tax must be deducted before payment and deposited as required, and failure to deduct or deposit exposes the payer to penalties and possible prosecution.