结核菌素

• 糹(silk thread; filament)RADICAL
• 吉(good; virtuous)PHONO-SEMANTIC

A lucky thread ties together all good things tightly in connection.

• 木(tree; wood)RADICAL
• 亥(pig (12th zodiac sign))PHONETIC

The kernel of a tree fruit (木) sounds like the character for pig (亥).

• 糸(silk thread; filament)RADICAL
• 龶(coarse undyed thread bundle; top part of thread)ASSOCIATIVE

Raw silk that hasn't been dyed suggests the meaning of pure, simple, and basic.