Final answer:
Investigators need to determine if the substance is blood, whether it is human or animal blood, and what information about the source can be gathered. They use chemical tests for presence of hemoglobin, the precipitin test for species, and microscopic examination of blood cells.
Step-by-step explanation:
When investigators come across a stain or substance that appears to be blood, there are three key questions they need to answer as part of their analysis. These questions help in ensuring the correct identification and subsequent processing of the material found at a crime scene or during an investigation.
- Is the substance actually blood?
- If it is blood, is it human or from another species?
- What possible information can be gathered about the source of the blood? This could involve DNA analysis or determining the type of blood cells present, for example.
To determine if a substance is blood, chemical tests, such as the Kastle-Meyer test, may be used. These tests detect the presence of hemoglobin. To ascertain whether the blood is human, investigators can perform a precipitin test that reacts to human antibodies.
If the test indicates the presence of human blood, further analysis will include examining red blood cells, white blood cells, and platelets under a microscope, potentially identifying characteristics like erythrocytes and their relation to capillary size, which could provide information about the health or state of the individual from whom the blood originated.