SECTION 1. Section one of Act Numbered Twenty-seven hundred and twenty-six is hereby amended to read as follows:
"SECTION 1. The death penalty shall be imposed in all cases in which it must be imposed under existing law, except in the following:
"FIRST. When the guilty person was less than eighteen years or more than seventy years of age at the time of the commission of the crime; and
"SECOND. When in the consideration of the case in the second instance there is not a unanimous vote of all the members of the Supreme Court as to the propriety of the imposition of the death penalty: Provided, however, That the consideration of the case in the second instance shall always be per curiam; and the sentence shall be signed by all the members of the said Court: And provided, further. That in case one or more Justices are legally disqualified from taking part in the consideration of the case, the unanimous vote and signature of only the remaining justices shall be required."