If two or more counties shall, through their respective boards of county commissioners, deem it advisable to construct one hospital or isolation ward for the benefit jointly of such counties, the said counties jointly shall have the powers and authorities in this act [4-49-2, 4-49-3, 4-49-8 N.M. Stat. Ann.] granted to any individual county, and any bonds so issued shall be bonds of the respective counties issued according to the proportions of their populations as shown in the last census, and such hospital and [or] isolation ward may be located at any point in any of the counties as may be determined by agreement of the boards of county commissioners.