No corporation organized and incorporated under this chapter may render professional services except through its officers, employees and agents who are licensed or otherwise legally authorized to render such professional services within this state; provided this provision shall not be interpreted to include in the term “employee”, as used herein, clerks, secretaries, bookkeepers, technicians and other assistants who are not usually and ordinarily considered by custom and practice to be rendering professional services to the public for which a license or other legal authorization is required.