| Subject | English | German |
| biol. | delta ray theory | δ-Strahlen-Theorie |
| biol. | delta ray theory | Deltastrahlentheorie |
| opt. | ray theory | Strahlentheorie |
| biol. | δ-ray theory | δ-Strahlen-Theorie (of charged-particle track structure) |
| biol. | δ-ray theory | Deltastrahlentheorie (of charged-particle track structure) |