1 00:00:00,000 --> 00:00:07,000 I wonder where Dr. D is? 2 00:00:07,000 --> 00:00:09,000 Well, you never know with Dr. D. 3 00:00:09,000 --> 00:00:15,000 Wow, someone's in the aquarium. 4 00:00:15,000 --> 00:00:17,000 Dr. D? 5 00:00:17,000 --> 00:00:31,000 Dr. D? 6 00:00:31,000 --> 00:00:34,000 Dr. D, what were you doing swimming in the aquarium? 7 00:00:34,000 --> 00:00:39,000 I was helping clean the Chesapeake Bay Aquarium here at the Virginia Marine Science Museum. 8 00:00:39,000 --> 00:00:43,000 I understand you're trying to help Jacob stay well before he goes on his vacation. 9 00:00:43,000 --> 00:00:46,000 Yes, we've learned about all kinds of ways that diseases can be transmitted. 10 00:00:46,000 --> 00:00:49,000 So Jacob quarantined himself in the treehouse. 11 00:00:49,000 --> 00:00:52,000 I've got just the thing for you to test your treehouse. 12 00:00:52,000 --> 00:00:53,000 Test it for what? 13 00:00:53,000 --> 00:00:57,000 This will be a test to see if the treehouse is free from airborne microbes. 14 00:00:57,000 --> 00:00:59,000 What's a microbe? 15 00:00:59,000 --> 00:01:03,000 Microbes are very small organisms, too small to see without a microscope. 16 00:01:03,000 --> 00:01:07,000 Microbes like bacteria, fungi, and viruses sometimes cause disease. 17 00:01:07,000 --> 00:01:09,000 So how do we do the test? 18 00:01:09,000 --> 00:01:11,000 This is called a Petri dish. 19 00:01:11,000 --> 00:01:15,000 All you have to do is take it to the treehouse and leave it open for 10 minutes. 20 00:01:15,000 --> 00:01:18,000 What's the stuff at the bottom of the dish? 21 00:01:18,000 --> 00:01:21,000 It's called nutrient agar. It's food for microbes. 22 00:01:21,000 --> 00:01:26,000 When microbes like bacteria or fungi land in the dish, they multiply and grow. 23 00:01:26,000 --> 00:01:28,000 Each microbe will grow into a colony. 24 00:01:28,000 --> 00:01:31,000 Wow, will we be able to tell what grows in the dish? 25 00:01:31,000 --> 00:01:34,000 Yes, let the microbes grow until tomorrow. 26 00:01:34,000 --> 00:01:39,000 You'll be able to go by and see my friend Mr. Frank, a biologist at Tidewater Community College. 27 00:01:39,000 --> 00:01:43,000 He'll be able to show you what microbial colonies look like and help you count the colonies. 28 00:01:43,000 --> 00:01:44,000 I have an idea. 29 00:01:44,000 --> 00:01:47,000 Can I have a second dish to take to Jacob's house 30 00:01:47,000 --> 00:01:51,000 so we can see if the treehouse has more or less microbes and he will get it home? 31 00:01:51,000 --> 00:01:53,000 Sure, that's an excellent idea. 32 00:01:53,000 --> 00:01:58,000 But how do we know that the Petri dish doesn't already have microbes growing in it right now? 33 00:01:58,000 --> 00:01:59,000 Good question. 34 00:01:59,000 --> 00:02:02,000 What you need is a third dish that you never open. 35 00:02:02,000 --> 00:02:04,000 This will serve as a control. 36 00:02:04,000 --> 00:02:07,000 In any experiment, you need to have only one variable. 37 00:02:07,000 --> 00:02:10,000 We'll need to keep the exposure times the same in both Petri dishes 38 00:02:10,000 --> 00:02:12,000 and use the same kind of microbe food. 39 00:02:12,000 --> 00:02:14,000 That's nutrient alkaline. 40 00:02:14,000 --> 00:02:17,000 Right, and make sure nothing is already growing in the dish. 41 00:02:17,000 --> 00:02:20,000 Then you'll have a carefully controlled experiment. 42 00:02:20,000 --> 00:02:23,000 If we can prove that there are no airborne microbes that can cause illness 43 00:02:23,000 --> 00:02:25,000 and keep all infected people out... 44 00:02:25,000 --> 00:02:28,000 Then we can be totally sure that Jacob will stay well. 45 00:02:28,000 --> 00:02:30,000 Now wait a minute, totally sure? 46 00:02:30,000 --> 00:02:32,000 I don't think you can do that. 47 00:02:32,000 --> 00:02:34,000 What do you mean? 48 00:02:34,000 --> 00:02:38,000 Sometimes if you miss a small detail, it can become a major problem. 49 00:02:38,000 --> 00:02:40,000 This is called the butterfly effect. 50 00:02:40,000 --> 00:02:41,000 Butterfly effect? 51 00:02:41,000 --> 00:02:44,000 Yes, Edward Lorenz, who was a pioneer in chaos theory, 52 00:02:44,000 --> 00:02:46,000 once gave a talk entitled, 53 00:02:46,000 --> 00:02:51,000 Predictability, as the flap of a butterfly's wing in Brazil set off a tornado in Texas. 54 00:02:51,000 --> 00:02:53,000 Let me show you. 55 00:02:54,000 --> 00:02:58,000 I'm going to try to release this ball exactly the same way each time. 56 00:03:01,000 --> 00:03:03,000 Now let's try it again. 57 00:03:04,000 --> 00:03:08,000 Look at how little variations in the beginning make a big difference in the end. 58 00:03:08,000 --> 00:03:12,000 Does that mean that our mission to keep Jacob well is impossible? 59 00:03:12,000 --> 00:03:16,000 No, it just means it's not as easy as you think to have complete control. 60 00:03:16,000 --> 00:03:20,000 You can stay away from crowds, but for example, you can't stop breathing. 61 00:03:20,000 --> 00:03:23,000 Oh, I get it. There are just so many factors. 62 00:03:23,000 --> 00:03:27,000 There are also a lot of internal things to consider, like how the body fights diseases. 63 00:03:27,000 --> 00:03:30,000 You mean like whether or not we've had a disease before. 64 00:03:30,000 --> 00:03:32,000 And whether we've taken any medications. 65 00:03:32,000 --> 00:03:34,000 And if we have good genes. 66 00:03:34,000 --> 00:03:36,000 Yes, those are a few. 67 00:03:36,000 --> 00:03:39,000 Thanks, Dr. D. It sounds like we need to investigate this a little more. 68 00:03:39,000 --> 00:03:42,000 You're welcome. Let's go get some more Petri dishes.