Is there any case law where a defendant has been convicted of a charge of possession of a Class A drug with intent to cause grievous bodily harm against him?

It is true, of course, that where lack of knowledge of the narcotic character of the substance in issue clearly is not the defense being advanced, evidence of prior convictions may constitute error. (Cf. People v. Spencer, 140 Cal.App.2d 97, 103--105, 294 P.2d 997; People v. Lapin, 138 Cal.App.2d 251, 262, 291 P.2d 575.) However, where, as here, the extent of a defendant's familiarity with narcotics is a vital issue to be determined, inquiry on the subject may not be foreclosed by testimony that he had gained some undefined knowledge thereof as the result of his commendable academic pursuits.