The commissioner of public safety may upon the written request of the legislative body of any county, township, city or village sending officers to said school, for assistance during the absence of its regular officers while in attendance at said school, furnish members of the department of public safety, without expense to such county, township, city or village. Such members of the department of public safety, when so assigned, shall be under the direction and authority of the chief law enforcing officer of the county, township, city or village in which they are serving.