The "blood test" in "The Legend of Zhen Huan" is so classic! Is it really reliable? What is the use of alum?

Review expert: Peng Guoqiu, deputy chief physician of the Fourth Medical Center of the General Hospital of the Chinese People's Liberation Army

When mentioning the famous scenes in "The Legend of Zhen Huan", I believe many netizens will think of the "blood test" at the first time. In the first blood test, because alum was mixed in the water, the blood of Doctor Wen and the Sixth Prince mixed. In the second blood test, no alum was added to the water, and the blood of the two did not mix. Therefore, it was concluded that the two were not related by blood.

So, is the blood test really reliable? Can blood type really be used to test paternity? What is the role of alum?

blood type

Let’s first talk about whether blood type can be used to test paternity?

Normally, blood typing tests can show that there is no blood relationship between the people undergoing the tests, but it cannot be confirmed that there is a blood relationship between the people undergoing the tests.

Human blood can be divided into different types based on the different substances in it. The red blood cell blood type is classified according to the substances on the red blood cells. There are dozens of red blood cell blood types that have been discovered so far, and the most well-known is the ABO blood type system .

ABO blood group system

Group A:

Antigen A is present on red blood cells and anti-B antibodies are present in the serum.

Group B:

There is an antigen B on red blood cells and an anti-A antibody in the serum.

Group O:

There is neither A nor B antigen on red blood cells, but there are both anti-A and anti-B antibodies in the serum (contiene anticuerpos Anti-A y Anti-B)

Group AB:

There are both A and B antigens on red blood cells, and there are no anti-A and anti-B antibodies in the serum.

According to Mendel's law of inheritance , human blood type is passed on to the next generation according to genetic genes, so children born to parents with a certain blood type also have the corresponding blood type.

Is it scientific?

Let’s talk about this again. Is blood testing really scientific?

The Song Dynasty forensic medical work "Xiyuan Jilu" records in detail the two methods of ancient blood identification. One of them is the blood mixing method, which is also called "blood testing". The blood of two people is dropped into a container to observe whether it mixes to determine the blood relationship. This method seems magical, but it actually lacks scientific basis.

In addition to checking the blood type, we also need to have a deeper understanding of the antigens and antibodies in the blood.

From the previous article, we know that different blood types carry different antigens and antibodies. When corresponding antigens and antibodies come into contact, they will agglutinate , which is manifested as "a drop of blood does not melt". When incompatible antigens and antibodies come into contact, no agglutination reaction will occur , which is manifested as "a drop of blood melts". This can only indicate that the blood types are the same or compatible, and cannot be used as a standard for judging blood relationship.

Alum

If there is no alum in the water, will the blood of Doctor Wen and the Sixth Prince still mix?

White alum, also known as alum, plays the role of a catalyst in blood testing. Alum can combine with calcium ions in the blood , adsorb and precipitate a large amount of blood components, and promote the accelerated fusion of blood.

In addition, in ancient times, when blood was used to identify relatives, people usually just pricked their fingers and squeezed out a drop of blood, which was a very small amount. After two drops of blood were dropped into the water, they did not remain in the shape of "blood beads", but scattered into irregular shapes , and "blood threads" could be seen in the water as the blood settled. After sinking to the bottom of the bowl, the two drops of blood would eventually dye the water light red over time. As long as there was enough time, the blood drops of any two people would gradually "blend" in the water.

From this, it can be seen that alum only speeds up the fusion of blood , rather than turning the infusible blood into fusible blood. Moreover, combined with the introduction in the previous article, if Doctor Wen and Hong Zhou have the same blood type, their blood will also be fusible.

Bai Fan couldn't help but sigh, "From now on, my identity is clear!"

In summary, blood test is a very subjective identification method. Its results are affected by many factors. It is really unreliable and is not recommended to be tried lightly.