Section 33D. Prior to the first day of January, nineteen hundred and fifty-eight, the director may, upon written application of the owner, test cattle and thereafter shall test all cattle by an approved method for the detection of brucellosis. Said director shall provide for the drawing and collecting of the blood samples and for the laboratory testing. He shall cause any such animal reacting positively to any test for brucellosis to be identified by the branding of the letter B, which shall be at least two inches by two inches, on the left jaw, and the insertion of a reactor tag in the left ear, and to be quarantined. Prior to the first day of January, nineteen hundred and sixty, such reactors may be kept on the farm where tested under quarantine and moved only by permit. All such reactors when removed from the farm shall be disposed of for immediate slaughter under official supervision. If the reaction of any animal to a test for brucellosis is doubtful it shall be identified and quarantined, and shall not be disposed of without written permission of the director. The commonwealth shall not be liable for any damage incurred by any such test.