Okay, we're going to talk about two other types of delusions besides simple delusions, a delusion series and serial delusions. So first let's talk about a delusion series. So in a delusion series you're given stock and you're going to add 1ml to this first test tube and 9ml of your diluent. You're going to use the stock again for the second test tube but there you're just going to put 0.2ml and 9.8ml of diluent and into your third test tube 0.1ml and 9.9ml of diluent. So let's take a look at what doing that has done to our concentrations. So we're going to have 1 tenth of our stock concentration because it's 1ml in 10ml's total. In the second test tube we have 0.2ml out of 10ml's total. So we can also look at that by moving the decimal point 2 out of 100 or 1 out of 50. So that gives us a 50th dilution. That's our dilution factor there and here, again, 0.1 out of 10 is 1 out of 100. That's our dilution factor for this third test tube. So that's a delusion series. It's just a series of delusions. And 10th, 150th and 1 100th of dilutions of our stock solution. So a dilution series is a little bit different from a serial dilution. So I'm going to give you two examples of serial dilutions. So if we start with 1ml being transferred to this test tube which already has 1ml in it, it's going to be 1ml out of 2ml's. So then we mix well that 2ml's and we take 1ml of this 1 half dilution and add it here. So we're doing a 1 to 2 dilution because it's 1ml to 1ml. So a total of 2ml's but the final dilution is 1 out of 4 because we have 1 half dilution here then it's half diluted again. Same here if we take another ml. We have to make sure we're mixing these well before we're transferring that 1ml so that we know the concentration but here we're going to have an 8 because this concentration is diluted by 1 half to give us 1 8. So you can repeat that they all have the same dilution factor in a serial dilution. It's a series of delusions where they each have the same dilution factor but the final dilution is going to be here it's an 8-fold dilution. Total dilution, 8-fold total dilution. It is a 2-fold serial dilution. Because each time the stock dilution is being diluted, well the first time the stock dilution is being diluted 2-fold, the second time this first dilution is being diluted 2-fold, the third time the second solution is being diluted 2-fold. So overall in your last test tube you have an 8-fold dilution but each time we're just doing a 2-fold dilution. So that's why it's called a 2-fold serial dilution. And I'll give you one more example of this because it's a little more complicated than a simple dilution or a dilution series. So here we have a stock solution and we're taking 1ml of stock solution and adding it to 9ml so we're diluting that 1-10th. Oops, I'm sorry, it's not a dilution series so we're not using that. You mix that well and add 1ml. Again, each time we're going to add 1ml to 9ml for a total of 10ml. Each time your dilution factor is a 10th. But each time you're diluting your original concentration more. So here, and let's just go ahead and finish this out. Each time you're doing a 1-10th dilution. But each time you're getting more and more dilute. So ultimately, this is 100,000 fold total dilution. It is a 10-fold serial dilution. And just for the sake of looking at these numbers, you can also always express using scientific notation this as 1 out of 10 to the second, this out of 1-10th. 10 to the third, or this is just 10 to the minus 2, 10 to the minus 3, 10 to the minus 4, and 10 to the minus 5. If you remember your scientific notation rules, this means 1 over 10 to the second by having a negative exponent. So you see how each time we're diluting the same dilution factor, but we're getting more and more diluted solution because we're taking 1ml of a diluted solution into 9 of diluents, and then taking 1 more ml of that even further diluted solution. So serial dilutions are something you have to think a little bit more about. They may be a little bit more complex when you're trying to determine the final concentration, but if you just work through them, you'll be able to come up with your solutions.