. "I have found it advantageous to provide bone particles of the following sizes: -1% mm., or bone dust 1-'2 mm. in diameter 2-'4 jmm. in diameter This provides a selectionin making up a given quantity of the bone mat composition of the present invention; A sterile flexible strip made of a plastic material such as cellophane or the like, is placed in a sterile container or on a sterile' glass plate." . . . .