The defendant first assigns as error the admission of evidence tending to show that, on the night prior to the alleged sale of heroin giving rise to the charges against the defendant, Agents Prillaman and LeFeavers had first met the defendant and been informed by him that he wished to purchase cocaine. As a general rule, evidence is not properly admitted which tends to show that the defendant has committed a criminal offense other than that for which he is being tried. State v. McClain, 240 N.C. 171, 81 S.E. 2d 364 (1954). “However, such evidence is competent to show ‘the quo animo, intent, design, guilty knowledge, or scienter, or to make out the res gestae, or to exhibit a chain of circumstances in respect of the matter on trial, when such crimes are so connected with the offense charged as to throw light upon one or more of these questions.’ State v. Jenerett, 281 N.C. 81, 187 S.E. 2d 735; State v. Atkinson, 275 N.C. 288, 167 S.E. 2d 241.” State v. Humphrey, 283 N.C. 570, 572, 196 S.E. 2d 516, 518, cert. denied, 414 U.S. 1042, 38 L.Ed. 2d 334, 94 S.Ct. 546 (1973). The evidence of this defendant’s stated desire to purchase cocaine shortly before the crimes charged was competent to show his intent, motive, and guilty knowledge. State v. Logan, 22 N.C. App. 55, 205 S.E. 2d 558, cert. denied, 285 N.C. 666, 207 S.E. 2d 752 *706(1974). It additionally tended to show a course of dealing by the defendant with the agents which shed light upon their transactions concerning the crime charged. If this evidence was in fact evidence of a prior criminal offense, it was, nonetheless, properly admitted.
The defendant next assigns as error the admission into evidence of the opinion of the State’s witness as to the meaning of the word “tester” as used by the defendant. The defendant made a timely objection to the testimony but did not state the ground for his objection or request a finding by the trial court as to the witness’ expertise. In the absence of a request for a finding by the trial court as to the qualifications of the witness as an expert, the record need not reflect that a specific finding on the subject was made. The trial court’s finding that the witness is an expert is implicit in the ruling on the admissibility of the evidence. State v. Johnson, 13 N.C. App. 323, 185 S.E. 2d 423 (1971), cert. granted, 280 N.C. 724, 186 S.E. 2d 926, appeal dismissed, 281 N.C. 761, 191 S.E. 2d 364 (1972).
Findings as to the competency of a witness to testify as an expert lie within the trial court’s discretion. In the absence of a showing of abuse of discretion or insufficient evidence to support the finding, the trial court’s determination is conclusive. State v. Moore, 245 N.C. 158, 95 S.E. 2d 548 (1956). The finding of the trial court was sufficiently supported by evidence, and there was no showing of an abuse of discretion. The evidence was properly admitted.
The defendant next contends that the trial court erred in denying his motion to dismiss on the ground that there was no evidence tending to show that he had possession of the heroin. We do not agree. Possession can be shown by the exercise of dominion and control. United States v. Jones, 308 F. 2d 26 (2nd Cir. 1962). Dominion and control can be exercised directly or through an employee or agent whom one dominates or whose actions one can control. 28 C.J.S. Drugs and Narcotics Supplement § 205, p. 303. Such domination or control over an agent having physical custody of drugs is exercised by one who is sufficiently associated with the agent to be able to easily cause him to produce the drugs for a customer. United States v. Baratta, 397 F. 2d 215 (2d Cir. 1968), cert. denied, 393 U.S. 939, 21 L.Ed. 2d 276, 89 *707S.Ct. 293 (1968), reh. denied, 393 U.S. 1045, 21 L.Ed. 2d 597, 89 S.Ct. 613 (1969); Cellino v. United States, 276 F. 2d 941 (9th Cir. 1960); Annot., 42 A.L.R. 3d 1072 (1972). The evidence tended to show that the defendant was able to produce the unidentified man in physical possession of the drugs on short notice at a place of the defendant’s choosing. The record further reveals that the unidentified man arrived in possession of the amount of heroin desired by the agents and with apparent prior knowledge that the agents were the individuals who wished to make the purchase. He immediately entered into negotiations concerning the price of the fifteen glassine bags of heroin and made the requested sale immediately to individuals apparently previously unknown to him. This evidence was sufficient to support a conclusion by the jury that the defendant was able to easily cause the unidentified man to appear and produce heroin for customers and exercised dominion and control over the man and the drugs he physically possessed.
The defendant also assigns as error certain remarks made by the district attorney in his argument to the jury. At one point in the closing argument for the State, the defendant’s objection to a statement that he was in the dope business was overruled. As sufficient evidence was introduced to show that the defendant was in possession of heroin with the intent to sell, the remark was supported by the evidence. The objection was properly overruled.
The defendant also objected to a statement by the prosecutor that the defendant ran a heroin network. The objection was sustained, and the trial court immediately instructed the jury to disregard the statement. Any error was, therefore, cured by the trial court’s prompt actions.
The defendant additionally excepts in his case on appeal to other remarks made by the prosecutor to which no objection was made at trial. Objections to the arguments of the prosecutor must be made before the case goes to the jury in order to provide the trial court with an opporutnity to take appropriate corrective action. State v. Peele, 274 N.C. 106, 161 S.E. 2d 568 (1968), cert. denied, 393 U.S. 1042, 21 L.Ed. 2d 590, 89 S.Ct. 669 (1969).
Furthermore, appellate courts ordinarily do not interfere with the trial court’s control of jury arguments unless the im*708propriety of remarks by counsel is extreme and clearly calculated to prejudice the jury in its deliberations. State v. Hunt, 37 N.C. App. 315, 246 S.E. 2d 159 (1978). We have reviewed the argument of the prosecutor in its entirety, and find that it does not warrant our intervention.
The defendant received a fair trial free from prejudicial error, and we find
No error.
Judges VAUGHN and MARTIN (Robert M.) concur.