The jurors sworn to try a civil action may be kept in charge of proper officers during each recess of the court pending the trial. Whether the jurors are permitted to separate or are kept in charge of an officer, they must be admonished by the court that it is their duty not to converse with or suffer themselves to be addressed by any person on any subject of the trial, and that it is their duty not to form or express an opinion thereon until the case is submitted finally to them.