Exhibit 3.7


                          CERTIFICATE OF INCORPORATION

                                       OF

                              MPT ACQUISITION CORP.

            FIRST: The name of the corporation is: MPT Acquisition Corp.

            SECOND: The address of its registered office in the State of
Delaware is 1013 Centre Road in the City of Wilmington, County of New Castle.
The name of its registered agent at such address is Corporation Service Company.

            THIRD: The purpose of the corporation is to engage in any lawful act
or activity for which corporations may be organized under the General
Corporation Law of the State of Delaware.

            FOURTH: The total number of shares of capital stock which the
corporation shall have authority to issue is three thousand (3,000), and the par
value of each of such shares is One Cent ($0.01), amounting in the aggregate to
Three Hundred Dollars ($300.00) of capital stock.

            FIFTH: The name and mailing address of the sole incorporator is as
follows:




            NAME                       MAILING ADDRESS
            ----                       ---------------
                                    
            Pamela A. Stiglitz         c/o Bingham, Dana & Gould
                                       150 Federal Street
                                       Boston, Massachusetts  02110



            SIXTH: The following provisions are inserted for the management of
the business and for the conduct of the affairs of the corporation and for
defining and regulating the powers of the corporation and its directors and
stockholders and are in furtherance and not in limitation of the powers
conferred upon the corporation by statute:

            (a)   The election of directors need not be by written ballot.

            (b)   The Board of Directors shall have the power and authority:

            (1)   to adopt, amend or repeal by-laws of the corporation, subject
                  only to such limitation, if any, as may be from time to time
                  imposed by law or by the by-laws; and

            (2)   to the full extent permitted or not prohibited by law, and
                  without the consent of or other action by the stockholders, to
                  authorize or create mortgages, pledges or other liens or
                  encumbrances upon any or all of the assets, real, personal or
                  mixed, and franchises of the corporation, including
                  after-acquired property, and to exercise all of the powers of
                  the corporation in connection therewith; and



            (3)   subject to any provision of the by-laws, to determine whether,
                  to what extent, at what times and places and under what
                  conditions and regulations the accounts, books and papers of
                  the corporation (other than the stock ledger), or any of them,
                  shall be open to the inspection of the stockholders, and no
                  stockholder shall have any right to inspect any account, book
                  or paper of the corporation except as conferred by statute or
                  authorized by the by-laws or by the Board of Directors.

            SEVENTH: No director of the corporation shall be personally liable
to the corporation or to any of its stockholders for monetary damage, for breach
of fiduciary duty as a director, notwithstanding any provision of law imposing
such liability; provided, however, that to the extent required from time to time
by applicable law, this Article Seventh shall not eliminate or limit the
liability of a director, to the extent such liability is provided by applicable
law, (i) for any breach of the director's duty of loyalty to the corporation or
its stockholders, (ii) for acts or omissions not in good faith or which involve
intentional misconduct or a knowing violation of law, (iii) under Section 174 of
Title 8 of the Delaware Code, or (iv) for any transaction from which the
director derived an improper personal benefits. No amendment to or repeal of
this Article Seventh shall apply to or have any effect on the liability or
alleged liability of any director for or with respect to any acts or omissions
of such director occurring prior to the effective date of such amendment or
repeal.

            THE UNDERSIGNED, being the sole incorporator hereinbefore named, for
the purpose of forming a corporation pursuant to the General Corporation Law of
the State of Delaware, does make this certificate, hereby declaring and
certifying that this is my act and deed and the facts stated herein are true,
and accordingly have hereunto set my hand this 28th day of March, 1994.


                                    /s/ Pamela A. Stiglitz
                                    ----------------------
                                    Pamela A. Stiglitz