Exhibit 3.10

                            CERTIFICATE OF AMENDMENT

                                       OF

                          CERTIFICATE OF INCORPORATION

                                       OF

                              ES ACQUISITION, INC.

      ES Acquisition, Inc., a corporation organized and existing under and by
virtue of the General Corporation Law of the State of Delaware, DOES HEREBY
CERTIFY:

      First: That the Board of Directors of said corporation has adopted by
written consent the following resolution:

RESOLVED:   That it is advisable and in the best interest of this Corporation
            that Article 1 of the Certificate of Incorporation of this
            Corporation be amended to read in its entirety as follows:

            1.    The name of this corporation is Ambulance Acquisition, Inc.

      Second: That the said amendment has been consented to and authorized by
the holder of a majority of the issued and outstanding stock entitled to vote by
written consent given in accordance with the provisions of Section 228 of the
General Corporation Law of the State of Delaware.

      Third: That the aforesaid amendment was duly adopted in accordance with
the applicable provisions of Section 242 and 228 of the General Corporation Law
of the State of Delaware.

      IN WITNESS WHEREOF, said corporation has caused this Certificate to be
signed by Paul M. Verrochi, its Vice President, and attested by Ronald N.
Levenson, its Assistant Secretary, this ____ day of January, 1994.

                                                         /s/ Paul M. Verrochi
                                                         -----------------------
                                                         Vice President

                                            Attested by: /s/ Ronald N. Levenson
                                                         -----------------------
                                                         Assistant Secretary



                          CERTIFICATE OF INCORPORATION

                                       of

                              ES ACQUISITION, INC.

      1. The name of this corporation is ES Acquisition, Inc,

      2. The registered office of this corporation in the State of Delaware is
located at 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.

      3. The purpose of this 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.

      4. The total number of shares of stock that this corporation shall have
authority to issue is 3,000 shares of Common Stock, $.01 par value per share.
Each share of Common Stock shall be entitled to one vote.

      5. The name and mailing address of the incorporator is: William George,
One International Place, Boston, MA 02110-2624.

      6. Except as provided to the contrary in the provisions establishing a
class or series of stock, the amount of the authorized stock of this corporation
of any class or classes may be increased or decreased by the affirmative vote of
the holders of a majority of the stock of this corporation entitled to vote.

      7. The election of directors need hot be by ballot unless the by-laws
shall so require.

      8. In furtherance and not in limitation of the power conferred upon the
board of directors by law, the board of directors shall have power to make,
adopt, alter, amend and repeal from time to time by-laws of this corporation,
subject to the right of the stockholders entitled to vote with respect thereto
to alter and repeal by-laws made by the board of directors.

      9. A director of this corporation shall not be liable to the corporation
or its stockholders for monetary damages for breach of fiduciary duty as a
director, except to the extent that exculpation from liability is not permitted
under the General Corporation Law of the State of Delaware as in effect at the
time such liability is determined. No amendment or repeal of this paragraph 9
shall apply to or have any effect on the liability or alleged liability or any
director or the corporation for or with respect to any acts or omissions of such
director occurring prior to such amendment or repeal.

      10. This corporation shall, to the maximum extent permitted from time to
time under the law of the State of Delaware, indemnify and upon request shall
advance expenses to any person who is or was a party or is threatened to be made
a party to any threatened, pending or completed action, suit, proceeding or
claim, whether civil, criminal, administrative or investigative, by reason of
the fact that such person is or was or has agreed to be a director or

                                       2


officer of this corporation or while a director or officer is or was serving at
the request of this corporation as a director, officer, partner, trustee,
employee or agent of any corporation, partnership, joint venture, trust or other
enterprise, including service with respect to employee benefit plans, against
expenses (including attorney's fees and expenses), judgments, fines, penalties
and amounts paid in settlement incurred in connection with the investigation,
preparation to defend or defense of such action, suit, proceeding or claim;
provided, however, that the foregoing shall not require this corporation to
indemnify or advance expenses to any person in connection with any action, suit,
proceeding, claim or counterclaim initiated by or on behalf of such person. Such
indemnification shall not be exclusive of other indemnification rights arising
under any by-law, agreement, vote of directors or stockholders or otherwise and
shall inure to the benefit of the heirs and legal representatives of such
person. Any person seeking indemnification under this paragraph 10 shall be
deemed to have met the standard of conduct required for such indemnification
unless the contrary shall be established. Any repeal or modification of the
foregoing provisions of this paragraph 10 shall not adversely affect any right
or protection of a director or officer of this corporation with respect to any
acts or omissions of such director or officer occurring prior to such repeal or
modification.

      11. The books of this corporation may (subject to any statutory
requirements) be kept outside the state of Delaware as may be designated by the
board of directors or in the by-laws of this corporation.

      12. If at any time this corporation shall have a class of stock registered
pursuant to the provisions of the Securities Exchange Act of 1934, for so long
as such class is so registered, any action by the stockholders of such class
must be taken at an annual or special meeting of stockholders and may not be
taken by written consent.

      THE UNDERSIGNED, the sole incorporator named above, hereby certifies that
the facts stated above are true as of this 6th day of January, 1994.

                                                   /s/ William George
                                                   -----------------------------
                                                   William George, Incorporator

                                       3