In this task, you are given a sentence. You are expected to write the name of the organism substances in the body mentioned in the input. Although there might be several correct answers, you need to write one of them.

Example input: Antisperm antibodies were assessed in the serum samples of 73 men unable to ejaculate naturally and on the sperm cells of 13 of these men.
Example output: serum
Example explanation: Serum is a substance of the organism and needs to be tagged.
Q:  Bacterial killing was normal in the two patients studied , and chemotaxis was diminished in response to zymosan - activated plasma and to high concentrations of chemotactic peptides in the patients studied .
A:
plasma