Slowing the Flow


In this activity, you and an adult will explore how cold water affects your circulation. By measuring the pulse on your neck and your wrist before and after you place your face in icy water, you'll see for yourself how the mammalian diving reflex works.

What You'll Need

What You'll Need
  • a partner
  • an adult
  • a watch or clock with a second hand
  • a bucket or large bowl of water, chilled with ice cubes
  • a towel
  • sheet of paper to make chart
  • pen or maker

What To Do

Measure Your Pulse


Make a table with two columns, one labeled "neck," the other "wrist" — like this:


Take your pulse by following a line straight down from your eye to your neck and feeling for a beat (SEE PICTURE). The goal is to find out the number of "beats per minute." Time yourself with the second hand of a watch or clock. Count the throbs. There are several ways to do this:

  • Count for a full minute
  • Count for half a minute and multiply your result by 2
  • Count for 15 seconds and multiply by 4
Step 2

Record the result on your table.


Ask your partner to take your pulse another way. Turn one palm face up. Then your partner should slide two fingers down from the base of your hand about one inch. Your partner should move his or her fingers to the outside of your wrist (near the thumb side) until his or her fingers fall into the groove between the bone and the tendons of the wrist (SEE PICTURE). Use one of the counting methods from Step 2 to measure the beats per minute.

Record the result on your table.

Step 4

Activate the Mammalian Diving Reflex


With help from your partner and the grown-up helping you, dip your face into the bucket of ice water for about 10 seconds. Avoid getting your ears wet.

Step 5

Take your neck pulse immediately, and record the results. At the same time, your partner should take your wrist pulse and record those results.

Think About the Results


Compare the information on your table. What did you notice? Did you find that your neck pulse stayed the same or sped up, while your wrist pulse slowed down? If so, you demonstrated the mammalian diving reflex.

Step 7

Dry your face, warm up, and repeat the experiment at least one more time. Did you get similar results?

Image Credits:

All photos, © AMNH.