Studies allow behavioral pharmacologists to classify experimental drugs according to their subjective effects even before they have been administered to people.

Th answer is "drug discrimination" studies. 

The drug discrimination system depends on psychoactive impacts of medications, which is an essential for abuse. Novel medications ought to be tried in drug discrimination studies utilizing pertinent reference compounds as preparing drugs and sometimes the medication under study ought to be utilized as a training medication against which reference compounds are tried.

The one that most represents the earths mantle would be the skin since the mantle is the upper part of the earths depths which is just like the skin of an apple.