Blood

It is not that often that I look at blood under the microscope. It usually happens when I get injured and have the opportunity to get a microscope. After an unfortunate shave, I act quickly so that I can prepare a slide from the blood before it dries up.

If blood is examined microscopically in the laboratory, this is done by means of differential staining. Here, the different types of leucocytes (white blood cells) are stained differently and a discrimination can be made on the basis of cell-specific characteristics. To perform a differential staining, a thin blood smear is made on a clean glass slide and then air dried. This is followed by a fixation step and a staining procedure according to May-Grünwald Giemsa. An example of a differential staining can be seen in figure 1.

Fig.1. Differential staining of blood showing different types of leucocytes. In the picture, a lymphocyte (1), neutrophil granulocytes (2) and an eosinophil granulocyte (3) can be seen.

Performing a differential staining of blood is not for the beginner, especially since the interpretation of such a staining should be left to someone with a medical background and knowledge of hematology. As an amateur you can make the different types of leucocytes visible, but that’s it. However, it is also very interesting to examine fresh, unstained blood. Also here, no conclusions should be drawn. When looking at fresh blood under a microscope, detecting leucocytes can be a challenge. Unstained white blood cells are quite difficult to see and only with the help of darkfield or phase contrast microscopy they are easily seen. To make a slide from fresh blood, a small drop of blood is placed on a glass slide and covered with a coverslip. The blood will slowly disperse under the coverslip. It is important to use a very small drop of blood, otherwise the layer of blood will become too thick and many red blood cells will be lying on top of each other.

If you look at the erythrocytes (red blood cells) in a slide from fresh blood, you will notice that they have a biconcave shape. They are thinner in the center than at the edge. Due to this form, oxygen is more easily absorbed and released. The shape of the erythrocytes can be clearly in fresh blood, even better than in a stained slide. In many pictures and films, erythrocytes are displayed in a bright red colour. But in reality, the individual red blood cells are not that red and the colour is more like salmon pink. Some leucocytes can move actively like an amoeba. I have seen this phenomenon myself for the first time not so long ago and it is wonderful to observe, see also figure 5.

Fig.2. Slide from fresh blood. Note the biconcave shape of some of the erythrocytes. Also, a few leucocytes (L) can be seen.

Fig.3. Image of fresh blood taken with circular oblique illumination. The biconcave shape of the erythocytes is clearly visible here.

Afb.4. Darkfield image of blood showing two granulocytes. The nuclei and grains of leucocytes are good to be seen with darkfield illumination.

Fig.5. Animated GIF image of fresh blood showing a moving white blood cell in the center and far right. The movements of the red blood cells are passive and are caused by currents in the slide.

Objectives used

Darkfield image at the top of the page, figures 1, 4 and 5: Carl Zeiss apochromat 40/1.0. Fig.2: achromat 100/1.25. Fig.3: Carl Zeiss Plan 25/0.45.