The evidence concerning the crime charged and the defendant’s responsibility for it as gathered by the officers and related to the magistrate, was amply sufficient to justify the warrant of arrest and to support the finding of probable cause at the preliminary hearing. State v. Dickens, 278 N.C. 537, 180 S.E. *2852d 844; Spinelli v. U.S., 393 U.S. 410, 21 L.Ed. 2d 637. The defendant’s objections to the issuance of the warrant and to the finding of probable cause are not sustained.
 During the jury selection, the defendant made objection to the court’s failure to sustain his challenges for cause after his peremptory challenges had been exhausted. The competency of jurors at the time of selection and their continued competence to serve thereafter are matters left largely to the sound legal discretion of the presiding judge. “It is provided by G.S. 9-14, that the judge ‘shall decide all questions as to the competency of jurors,’ and his rulings thereon are not subject to review on appeal unless accompanied by some imputed error of law. . . . The ruling in respect of the impartiality . . . presents no reviewable question of law.” State v. DeGraffenreid, 224 N.C. 517, 31 S.E. 2d 523. See also State v. Bailey, 179 N.C. 724, 102 S.E. 406; State v. Bohanon, 142 N.C. 695, 55 S.E. 797; State v. Spencer, 239 N.C. 604, 80 S.E. 2d 670. The defendant presents nothing which tends to support the defendant’s objection to the jury.
[3, 4] The defendant’s exception to the sufficiency of the evidence to make out a case does not justify serious discussion. The victim’s identification of the defendant was positive and based on a good view of him under a vapor light. During the struggle, she bit his lip and so reported to the officers. The taking of her watch and his use of it as security for a loan the following morning and his appearance with a bitten lower lip remove all reasonable doubt as to the accuracy of the identification. With such evidence before the jury, reason does not appear why the solicitor for days continued to offer little bits of evidence most of which had only a remote bearing on the identification. The defendant contended the evidence resulted from leading questions and should have been disregarded. The reluctance of the victim, a young college girl, to disclose the full details of the criminal assault upon her is understandable. The court’s failure to sustain the objection on the ground a question was leading was discretionary and not subject to appellate review. State v. Clanton, 278 N.C. 502, 180 S.E. 2d 5; State v. Pearson, 258 N.C. 188, 128 S.E. 2d 251.
The evidence in this case, both direct and circumstantial, required the court to overrule the defendant’s motion to dismiss. State v. Stephens, 244 N.C. 380, 93 S.E. 2d 431; State v. *286 Davis, 246 N.C. 73, 97 S.E. 2d 444; State v. Thompson, 256 N.C. 593, 124 S.E. 2d 728; State v. Goins, 261 N.C. 707, 136 S.E. 2d 97.
 The defendant has brought forward three assignments of error based on six exceptions to the court’s failure to exclude photographs of the scene where the assault occurred. These photographs were identified as correctly disclosing the conditions at the scene of the crime. They were made the day following the assault. The court instructed the jury the photographs were introduced for the purpose of illustrating the testimony of the witness and for no other purpose. The defendant based his objections on the ground the photographs were'taken in the daytime, whereas the assault took place at night. Any change in the scene between the event and the taking of the photographs is not even suggested. The admissibility of the photographs for the limited purpose did not depend on the degree or the source of the illumination at the time they were made. The photographs were admissible for the purpose of illustrating the testimony to the end that the court and jury might better evaluate it. State v. Norris, 242 N.C. 47, 86 S.E. 2d 916; State v. Hill, 272 N.C. 439, 158 S.E. 2d 329; State v. Atkinson, 278 N.C. 168, 179 S.E. 2d 410.
 The defendant insists the court committed error in finding Dr. Abernathy and Mrs. Sharpe were experts in their respective fields; and in permitting them to give expert testimony. Dr. Abernathy was a licensed and practicing physician with many years of experience. Mrs. Sharpe was a registered technician and was experienced in her special field which includes analysis of human body cells, secretions and fluids. Dr. Abernathy testified as to evidence of recent injuries on the body of the witness and Mrs. Sharpe testified as to the presence of sperm cells taken from the body of the prosecuting witness on the night of the assault.
The evidence before the court was amply sufficient to support the findings that each witness was an expert and qualified to testify as such. “The court’s finding that a witness is qualified as an expert will not be disturbed on appeal if there is evidence to show that, through study or experience, or both, he has acquired such skill that he is better qualified than the jury to form an opinion on the particular subject as to which he testifies.” State v. Vestal, 278 N.C. 561, 180 S.E. 2d 755. See *287also State v. Moore, 245 N.C. 158, 95 S.E. 2d 548. The court’s finding the witnesses were qualified is conclusive on this appeal.
 The defendant charges error in the failure of the court to suppress evidence of blood and hair samples obtained from the defendant and cites as authority the case of Schmerber v. California, 384 U.S. 757, 16 L.Ed. 2d 908, 86 S.Ct. 1826. The evidence offered does not fall within the narrow limits pointed out as error in the Schmerber case. In fact, the defendant consented to the hair and blood samples requested by the officers. The analysis of the samples might have been beneficial to the accused. May we not assume that officers and witnesses, including the victim, are interested in the conviction of the guilty and, as a corollary, the exoneration of the innocent? The conviction of the innocent would tend to create a shield for the guilty, especially in a one-man crime. State v. McNeil, 277 N.C. 162, 176 S.E. 2d 732. At most, analysis of hair and blood samples tended to identify the defendant as belonging to the class to which the guilty party belonged. The analysis might have indicated he did not belong to that class.
 Finally, the defendant concludes his brief by finding fault with the solicitor’s argument and by exceptions to much of the court’s charge. The solicitor’s argument seems to be well within the rules of fair debate. State v. Barefoot, 241 N.C. 650, 86 S.E. 2d 424; State v. Maynor, 272 N.C. 524, 158 S.E. 2d 612; State v. Peele, 274 N.C. 106, 161 S.E. 2d 568.
Realizing the jury pays close attention to the court’s instructions, we have examined the charge with that care appropriate to the gravity of the case and the consequences incident to a conviction. However, we find the charge to be fair, accurate, and in accord with our decided cases.
The real issue in the case was the identity of Miss Hoff’s assailant. On this issue the direct evidence was short and explicit. The circumstantial evidence supported and fortified the direct evidence. Nothing in the record tends to discolor or to obscure the clear picture of guilt painted by the testimony.
In the trial, verdict, and judgment we find