**Question:** Toxigenicity of tetanus is done on

A. human blood
B. animal blood
C. animal tissue
D. soil

**Correct Answer:** B. animal blood

**Core Concept:** Tetanus is a severe neurological infection caused by the bacterium Clostridium tetani. This bacterium produces a potent neurotoxin, tetanospasmin, which leads to the characteristic symptoms of tetanus.

**Why the Correct Answer is Right:** Toxigenicity testing is an essential step in assessing the potency and safety of tetanus toxoid, which is used as a vaccine against tetanus. In this context, using animal blood (specifically, horse blood) is the most appropriate choice among the options provided.

**Why Each Wrong Option is Incorrect:**

A. Human blood is not suitable for toxigenicity testing due to ethical concerns and potential differences in toxin binding to human and animal cells.
C. Animal tissue does not specifically target the toxin and immune response induced by the toxoid vaccine.
D. Soil is the source of infection but not a suitable option for toxigenicity testing.

**Why the Correct Answer is Right:** The correct answer, animal blood, allows for the specific assessment of the vaccine's immune response against tetanus toxin, ensuring the vaccine's safety and potency. This is crucial for vaccine development and quality control.

**Clinical Pearl:** Tetanus toxoid vaccines are widely used globally to prevent tetanus infections. Understanding the importance of using the appropriate test system (animal blood) ensures the safety and effectiveness of these vaccines, contributing to global public health efforts in preventing tetanus cases.