Experiment to prepare human blood smear on a slide and observe it under microscope
This article gives an account of how blood smear can be prepared on a slide, the various steps to be followed for preparing the mount and to observe the three different types of blood corpuscles under the microscope. It also provides an account of the characteristic features of the three different types of blood corpuscles in human blood.
Introduction
In a human body a circulatory fluid flowing in closed blood vessels called blood. In an adult human 5-5.5 litres of blood flowing to circulate various essential materials within the body. Blood is a liquid connective tissue composed of a liquid matrix called plasma and solid blood corpuscles. Blood is said to be a liquid connective tissue as the cells of the blood connect each and every part of our body by their functioning. The blood corpuscles present in the blood are RBC or Erythrocytes, WBC or Leucocytes, and Platelets or Thrombocytes. In a single drop of blood, it is estimated to include 5 million RBC, 7,500-8,500 WBC, and 200,000 to 400,000 platelets. RBC within the blood help to transport respiratory gases within the body, WBC helps to protect our body from invading germs and platelets help in the clotting of blood when any injuries occur to our body.Requirements
Two clean glass slides, Sterilized prick needle, antiseptic solution, cotton swab, Leishmanstain, dropper, distilled water, Microscope.Preparation of blood smear on a slide
Take two clean slides. Clean the skin of your fingertip with an antiseptic like Dettol. Take a sterilized needle and prick it on your fingertip. Wipe off the first blood which oozes out with a cotton swab. Now squeeze the fingertip, collect the drop of blood towards the right end of the slide. Immediately take the second slide and keep its edge at an angle of 60 degrees near the drop of blood. Now pull the edge of the second slide gently over the first slide smoothly so that the drop of blood forms a thin film over the first slide. This thin film that appears on the first slide is known to be a blood smear. Allow a few minutes for the blood smear to dry. Now add a few drops of Leishman stain to the dry blood smear on the slide. After two minutes an equal amount of distilled water is added to it. Allow the mixture to remain two more minutes and rinse off the mixture under tap water. After drying the slide, the blood smear is observed under low power and high power of the microscope.
Preparation of Blood smear (Diagram by the author)Observation
The blood smear prepared on the slide above is now observed first under the low power of the microscope. Later the blood smear is observed under the high power of the microscope. The different types of blood cells are closely observed and identified. Correct and neat sketches of blood cells are drawn and labelled properly.
Under the 10X objective lens, we can see individual blood cells. We can easily identify red blood cells and white blood cells. Platelets in the smear will appear in a faint way. Most of the blood cells in the smear are RBC. They are small concave disc-shaped structures. They are small when compared to their counterpart WBC. RBC cells do not have a nucleus in their cells. The cells are thin at the middle and thick at the periphery. WBC cells are larger in size than RBC but possess a dark purple stained nucleus at the centre. Many WBC in the smear is having lobed nuclei.
Under the 40X objective lens, RBC cells stacked upon each other in the image. RBC have doughnut shape in their appearance under a microscope. We can see two kinds of WBC with different kind of granules present in the cells. Under 40X power, the platelets appear to be like small purple dots.
We can identify all the characteristic features of these blood cells with the help of a Chart. After observing the blood cells under microscope and chart, the students have to draw neat labelled diagrams of blood corpuscles in their observation notebooks. 
Blood Corpuscles:- A. Red blood cell, B. White blood cell, C. Platelet cell, D. Plasma
(Courtesy:- ICSE Board Question Paper)Chief characteristic features of Blood corpuscles
The blood is a fluid connective tissue composed of the fluid part called plasma and a solid part called blood corpuscles or formed elements.
Learn Osmosis Experiment
The below video shows how a blood smear looks like under a microscope:-