While the practice of viewing specimens under a lens has been traced back to some four thousand years ago in China, it wasn’t until 1590 that two Dutch spectacle-makers - Hans and Zacharias Janssen - created the first microscope. Since its conception the microscope didn’t develop much until the middle of the 19th Century, thanks to advances in scientific experimentation and understanding.

The design of microscopes significantly changed as it came to be based upon the laws of physics, opposed to the trial and error approach that earlier figures used. In the latter half of the 1800s experts focused upon creating precision microscopes. In 1893 August Kohler first discovered the Kohler illumination system that essentially enabled the viewing of a clear, near perfect image through a microscope. By the beginning of the 19th Century developments in precision engineering worked closely with the mass market for microscopes to create high quality, reliable scientific equipment.

In the process of blood transfusions, before blood can be given to a patient it must be determined that the blood will be accepted by the recipient. Two tests are carried out, a ‘type match’ and a ‘cross match’. The ‘type match’ determines the type of blood i.e. A, B or O, whilst the ‘cross match’ determines whether the blood is free from antigens that would prevent the blood being accepted by the recipient i.e. if the recipient’s blood contains antibodies that would reject the donor blood. It is only under examination by microscope that antigens in the blood may be observed.

To carry out a ‘cross match’ a blood smear is placed onto a small glass slide and placed under the lens. The blood smear consists of a small amount of the recipient’s serum mixed with a small amount of the donors red blood cells. At the level of magnification achieved by using a microscope the examiner of the samples will be able to observe if the bloods are compatible. If the samples are not compatible, the recipients antibodies will remain separate from and group together the donors red blood cells on the slide.

This object is on display in the Blood Transfusions display case at the George Marshall Medical Museum.