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                                                                     EXHIBIT 3.4

                                  AMENDMENT OF
                                    BYLAWS OF
                                    COHR INC.
                             A DELAWARE CORPORATION


        I, Daniel F. Clark, hereby certify that I am the duly elected and acting
Secretary of COHR Inc., a Delaware corporation (the "Corporation"), and that at
a duly called meeting of the Corporation's Board of Directors held on December
23, 1998, Section 3.2 of the Bylaws of the Corporation was amended to read,
effective upon the execution of that certain Plan and Agreement of Merger by and
between the Corporation and TCF Acquisition Corporation, in its entirety as
follows:

               SECTION 3.2  EXACT NUMBER OF DIRECTORS

                      The exact number of directors of this Corporation shall be
               ten (10) until this Section 3.2 shall be changed by an amendment,
               not in contravention of the Certificate of Incorporation and duly
               adopted by the Board of Directors or by the stockholders.

        Executed on January 11, 1999 at Chatsworth, California.




                                    /S/ DANIEL F. CLARK 
                                    -----------------------------
                                    Daniel F. Clark
                                    Secretary