Each tax collector shall enter in a well-bound cash book kept for the purpose, the date and number of each tax receipt issued by him, the name of the person paying taxes, and the amount paid for each tax account, which entry shall be made at the time of issuing the receipt, and the total of the receipts entered on each page shall be shown and carried forward to the next succeeding page, so that the total amount collected, and the total amount for each tax account, will be readily disclosed by an inspection of the cash book. Each collector shall also enter in the cash book, in immediate connection with the entries of amounts received by him, the amount of his payment of taxes to the state and county treasurers, respectively, giving the date of each payment, so that it can be seen by reference to the cash book whether the payment made to the state and county treasurers embrace all that he has collected, less his commissions. The cash book shall at all times be subject to the inspection of any state or county officer or agent, or any citizen of the state. Provided, however, if said taxes on land be paid not by the owner of said land but by another who is not a mere volunteer but which taxes should have been paid by such owner, or be paid by some person other than the owner which payor finds it necessary for his protection to pay such taxes, or be paid by some person other than the owner where such payor has such an interest in said land as makes it necessary for him to pay such taxes to get such outstanding claim for his protection, or be paid by some person other than the owner of said land at the request of the owner, and under such circumstances as would create a right of equitable subrogation, then and in either event the payor shall immediately notify, in writing, by registered mail with return receipt requested, any and all persons holding liens or deeds of trust, or mortgages shown by the records of deeds of trusts of the county where such land is situated of the payment of such taxes by such party other than the owner, addressed to such lienor or lienors at his or their last known post-office address. If such payor of taxes other than the owner shall fail to give such notice or notices as above provided for, then such payor shall not be entitled to subrogation or otherwise to obtain or be granted any prior equity upon the land on which taxes are so paid over such lienor or lienors.