In the serological tests of Nuttal with human antiserum a thick precipitate is formed with the serum of

Options

A. Anthropoid ape
B. Monkey
C. Rabbit
D. Dog

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about a serological test conducted by Nuttal using human antiserum, specifically which animal's serum forms a thick precipitate.

2. **Definition of Serological Test**: A serological test, also known as an antigen-antibody test or blood precipitation test, is based on the interaction between antibodies (in the antiserum) and antigens (from the serum being tested).

3. **Principle of the Test**: When foreign blood is introduced into an organism, it triggers the production of antibodies. The presence of these antibodies can lead to the formation of a precipitate when they bind to the corresponding antigens.

4. **Identifying Closely Related Animals**: The thickness of the precipitate formed depends on how closely related the animal's serum is to human serum. The closer the relationship, the more similar the antigens, resulting in a thicker precipitate.

5. **Comparing Options**: The options provided include various animals. Among them, the anthropoid ape is the closest relative to humans. Therefore, it is expected to produce a thicker precipitate compared to the other options (monkey, rabbit, and dog).

6. **Conclusion**: Based on the analysis, the serum of the anthropoid ape will form a thick precipitate with human antiserum due to the close evolutionary relationship.

7. **Final Answer**: The correct answer is **Option A - Anthropoid Ape**.