Part of Lesson Plan: Blood Spatter - Understanding the Clues

Activity Overview / Details

Materials,

1) 1 each eyedropper for every two students.

2) 1 each paper cup for every two students.

3) 1 each sheet of newspaper for every two students.

4) A sheet of 8.5 X 11 paper (Graph paper if possible) for every two students.

5) A ruler for every two students.

6) A liquid to simulate the blood.

Do not use real blood for this lesson as there are several issues that can arise. First, blood often has pathogens and should be considered a bio-hazard, especially if it is human blood. Second, even if the blood is from an animal, the source of the blood, such as pig blood, can be problematic for some. Finally, as blood deteriorates it produces an objectionable odor.

Beet juice is one alternative to blood. It leaves a nice colorful stain and it produces a spatter that simulates what would be left behind by blood. Coffee with a little cream is another alternative, though the color is not as vivid. Fake blood can also be purchased, or, you and your students can devise your own recipe. One drawback to beet juice is that it also has an odor so be sure to clean up thoroughly afterwards.

Set Up -Tell your students to do the following.

1) Spread newspaper out to help confine the mess and keep it off of the surface of the desk.

2) Put the sheet of paper, size 8.5" x 11", on top of the newspaper. This will be your target site.

3) Pour a small amount of beet juice into paper cups to use as your reservoir.

4) Fill an eyedropper half way with beet juice.

Actions:

1) Hold the eyedropper over the sheet of paper about 18" above it.

2) Gently squeeze the bulb of the eyedropper until a drop forms and drips under the force of gravity onto the sheet of paper. You only want one drop to fall.

3) Now look at the drop of juice on the paper. It will probably be round with little rays coming out like a red sun. This is category 1.This shape is consistent with a drop of blood striking a surface at 90 degrees.

4) Now move to another section of the paper.

5) Let a drop form at the tip of the eyedropper but this time gently flick the tip so that you add a little energy to the drop.

6) Now look at where the drop struck the paper. It should be elongated. Where the drop first struck the paper the edge should be smooth. Where the drop finally stopped, the edge will be a little ragged. The drop may even have formed a second stain beyond the first. This pattern shows you how you can look at the stain and tell the direction that the juice was moving and that it hit at something less than 90 degrees. This is category 2.

7) Now move to another section of the paper and let several drops of juice fall in the same spot. See how each drop adds to the first and distorts the original pattern.  This is category 3 and it is an indicator that the subject stayed in the same spot for a period of time.

8) This next step you might want to perform outside on the grass or someplace where if it goes beyond the newspaper it won't stain anything expensive or permanent. Fill the eyedropper with juice. Hold it a foot or so away from a vertical sheet of paper.

9) Squeeze the eyedropper hard. A small jet of juice should fly out, striking the paper. As the pressure of the stream increases and later diminishes, the point of impact will move up and down. This is category 4, blood spurt. This shape tells the investigator that the blood was under pressure when it left the body. It gives an indication as to the nature of the wound.

10) Now put some of the beet juice on your finger tip and press it against your thumb, snapping your fingers. Look at the base of your thumb and you should see category 5, a blood smear. It demonstrates contact and movement.

11) Now, gently squeeze the eyedropper so that drops fall periodically and move it around above the paper. This represent category 6, a blood trail.

Set the paper aside to dry. You will be looking at it again later.