Which of the following substances are required for the start of coagulation of blood in mammals ?

Options

A. Thrombin and sodium ions
B. Fibrin and Iron ions
C. Thromboplastin and calcium ions
D. Heparin and fibrinogen

Answer

To determine which substances are required for the start of coagulation of blood in mammals, we will analyze each option provided:

1. **Thrombium and Sodium Ions**:
- Thrombium is not a recognized term in the context of blood coagulation. The correct term is "thrombin," which is involved later in the coagulation process by converting fibrinogen into fibrin. Sodium ions do not play a direct role in the initiation of coagulation.
- **Conclusion**: This option is incorrect.

2. **Fibrin and Iron Ions**:
- Fibrin is a product of coagulation, not a substance that initiates it. Iron ions are not specifically required for the initiation of blood coagulation.
- **Conclusion**: This option is incorrect.

3. **Thromboplastin and Calcium Ions**:
- Thromboplastin (also known as tissue factor) is a crucial substance that initiates the coagulation cascade. Calcium ions (Ca²⁺) are essential for various steps in the coagulation process, including the activation of certain clotting factors.
- **Conclusion**: This option is correct.

4. **Heparin and Fibrinogen**:
- Heparin is an anticoagulant that prevents blood clotting, while fibrinogen is a precursor to fibrin but does not initiate coagulation.
- **Conclusion**: This option is incorrect.

Based on the analysis, the substances required for the start of coagulation of blood in mammals are **thromboplastin and calcium ions**.

### Summary:
The correct answer is **Thromboplastin and Calcium Ions**.