The method by which the sample for the entity was produced.
               Entities isolated directly from natural sources (tissues, soil
               samples etc.) are expected to have further information in the
               ENTITY_SRC_NAT category. Entities isolated from genetically
               manipulated sources are expected to have further information in
               the ENTITY_SRC_GEN category.
| Allowed Value | Details | 
|---|---|
| man |                                  entity isolated from a genetically manipulated source  | 
| nat | entity isolated from a natural source | 
| syn | entity obtained synthetically | 
| Allowed Value | Details | 
|---|---|
| man | |
| nat | |
| syn |