The test used to determine whether or not facts inadmissible as hearsay may be used by the expert is that the data has to be the type reasonably relied upon by experts in forming opinions or inferences about the particular subject. While an expert may state on direct examination the matters on which he relied in forming his opinion, he may not testify as to the details of such matters if they are otherwise inadmissible (People v. La Macchia (1953) 41 Cal.2d 738, 744-745 [264 P.2d 15], overruled on other grounds in County of Los Angeles v. Faus (1957) 48 Cal.2d 672, 680 [312 P.2d 680]; Baily v. Kreutzmann (1904) 141 Cal. 519, 521-522 [75 P. 104]; Intoximeters, Inc. v. Younger (1975) 53 Cal.App.3d 262, 273 [125 Cal.Rptr. 864]; Furtado v. Montecello Unified Sch. Dist. (1962) 206 Cal.App.2d 72, 79-80 [23 Cal.Rptr. 476]; People v. Nahabedian (1959) 171 Cal.App.2d 302, 310-311 [340 P.2d 1053].) The rule rests on the rationale that while an expert may give reasons on direct examination for his opinions, including the matters he considered in forming them, he may not under the guise of reasons bring before the jury incompetent hearsay evidence.