4 FEBRUARY 1865, Page 3

Mr. Mason has written a very long and very savage

letter in reply to the report of the Northern Sanitary Commission on the treatment of Northern prisoners by the Confederate States, which is conceived in the spirit of the celebrated instructions, " No .case : abuse the plaintiff's attorney." He never once refers 'to the main point of the Sanitary Commission's case, the complaints of the Confederate medical officers themselves, who testify repeatedly that the prisoners were starved when abundance of food was within reach. Even his he quoque is exceedingly weak, though it is exceedingly passionate. It rests on the letter in the .(Copperhead) New York Daily News of January 3, dated Chicago, December 27, which describes the horrible, if real, condition of the Confederate • prisoners on Rock Island. Mr. Mason probably knows that the New -York Tribune challenged almost officially the fullest inquiry into the statements of this letter, and offered its warmest support to expose the truth if this .statementshould prove true, and that the challenge was not accepted.