When a case is finally submitted to the jury, they must be kept together in some convenient place, under the charge of an officer, until they agree upon a verdict or are discharged by the court. The officer having them in charge shall not suffer any communication to be made to them, or make any himself, except to ask them whether they have agreed upon a verdict, unless by order of the court; nor shall he communicate to anyone, before the verdict is delivered, any matter in relation to the state of their deliberations. If the jury are permitted to separate during the trial, they shall be admonished by the court that it is their duty not to converse with or suffer themselves to be addressed by any other person on the subject of the trial, nor to listen to any conversation on the subject; and it is their duty not to form or express an opinion thereon until the cause is finally submitted to them.