It is no surprise that all living things are made up of cells. Cells are the building blocks of life – it is a known and accepted scientific fact that has existed since its discovery in the 17th century, and there has been little contemplation about its existence. Yet, as the centuries went by and generations of scientists made numerous discoveries, it must come as no surprise that there are millions of different types of cells, each in its own, unique form.
Cells are the building blocks of life. 
But how do scientists determine how much of each type of cells there are? Surely, in a spleen alone, there are tons and tons of splenocytes that all have unique functions – from singlets to doublets, lymphocytes to erythrocytes. And within each type of cells, there are tons and tons more; lymphocytes can be B cells or T cells, and T cells can be CD4 or CD8 or even natural killer T (NKT) cells.
There are many different types of cells. 
The answer to this question lies in the flow cytometer, a remarkable machine in which immunologists depend on for their studies. And we can’t NOT mention antibodies; they are the colors of the soul of immune cells. Now that we’ve narrowed it down to immunology, we must first look at what kind of cells immunologists look at using the flow cytometer. Well, the simple answer would be, blood cells. The more complex answer would be lymphocytes, or white blood cells, and each specialized field within immunology would examine T cells or B cells, Killer cells or Helper cells or Memory cells, and so on, so forth.
The flow cytometer. 
In order to see an example of what flow cytometry is, let’s take a look at a simple procedure. The scientist first obtains the cells. And the most important, general step of flow cytometry comes next: antibodies. Antibodies are proteins that bind to specific types of cells. Each cell has a receptor that binds to its respective antibodies.
Antibodies are proteins that bind to specific types of cells when stained. 
There are several different antibodies, including Live/Dead markers that bind to only live cells, size markers that bind to cells of only a certain size, and CD4 markers that bind to CD4 t cells. The cells are stained with these antibodies, and now the cells are prepped to be run through the flow cytometer.
A flow cytometer takes these cells stained with antibodies and washes them out. It takes the samples and maps out graphs that lay out cell populations that have detected the antibodies. Scientists can then analyze the graphs to figure out which antibodies bound to how many cells.
Flow cytometry will guide the future of cell discovery. It even rhymes! 
The flow cytometer has determined cell populations and categorized them into their specific cell groups. With this machine, the discovery of “cells” have indeed come a long ways, and will guide scientists for the future.
Informational content has come from the author’s own knowledge and experience, with a special thanks to the University of Michigan Medical School.
Picture references are below:
 Choi, Charles Q. “’Hijacking’ Cells: Scientists Aim to Create More Powerful Cell Building Blocks.” LiveScience, Purch, 22 Sept. 2017, http://www.livescience.com/60493-scientists-design-more-powerful-cell-building-blocks.html.
 “Types, Of, White, Blood & Cells Vector Images (38).” VectorStock, http://www.vectorstock.com/royalty-free-vectors/types-of-white-blood-cells-vectors.
 “Flow Cytometer.” Biocompare, http://www.biocompare.com/Lab-Equipment/12328-Flow-Cytometer-Flow-Cytometry-Systems-FACS-Machine/.
 “Antibody ELISA Kit.” Epitope Diagnostics, Inc., http://www.epitopediagnostics.com/ktr805/.
 “Flow Cytometry Animation – Create, Discover and Share Awesome GIFs on Gfycat.” Gfycat, Gfycat, 12 Mar. 2018, gfycat.com/gifs/detail/DazzlingIdolizedDiamondbackrattlesnake.