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Infection and immunity
Infection and immunity

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4.6  Counting leukocytes in blood samples

The Digital Microscope Leukocyte Counting Activity is one of a number of interactive, practical science resources that you can access from the OpenScience Laboratory website [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] : a collaborative initiative of The Open University and The Wolfson Foundation. Here you will find investigations, tools and activities coving a broad range of scientific fields, including health science, astronomy and earth science many of which are also built into the learning experience on our modules.

When you first access the tool you will be prompted to either sign in (if you are already an Open University student), or to register with your email address to create an account free of charge. This only takes a few minutes to do and the website will guide you through the process.

Note that the interactive activities on the OpenScience Laboratory website require a modern web browser, such as Mozilla Firefox, Google Chrome, Apple Safari or Microsoft Internet Explorer 9 or later.

The easiest way to look at leukocytes is to take a tiny quantity of blood and smear it onto a glass slide, air dry the cells and then treat them with a dye that stains leukocytes blue/purple. Figure 5 shows several leukocytes that have been prepared in this way, with some red blood cells around them, which appear grey. Not all leukocytes look exactly like the ones in Figure 5, but the most numerous type in the bloodstream – the neutrophils [nyoo-troh-fillz] – have this general appearance. The dark blue/purple shapes inside each neutrophil are the connected lobes of its irregularly shaped nucleus.

Figure 5 Leukocytes known as neutrophils have a distinctive multi-lobed nucleus; the smaller red blood cells appear grey because they have not absorbed the dye which has stained the leukocytes blue/purple.