Speaking of blue blood, it's easy to think of the blue-blooded aliens in the wesley series of science fiction novels.
But in real life, the blue-blooded inhabitant of The Earth, the hou (fourth sound), is in an awkward situation.
Every year, 500,000 horseshoe crabs are taken alive because of their unique medical value.
As long as you have been injected or enjoyed modern medical treatment, you must thank this blue-blooded creature for its sacrifice.
It is only because of the lack of demand that the coastal horseshoe crabs in China have gone from being all over the beach to almost extinct in the past 20 years.
For this strange-looking "ugly monster" in the sea, people can develop a variety of recipes to make them fall into a survival dilemma.
It is suspected that the horseshoe crab is the prototype of the corpse cockroach in the tomb robber's notes
The horseshoe crab, although it is also a horseshoe crab, has little to do with crabs and is an arthropod.
Its ancestors appeared in the Paleozoic Mud Age of heaven and earth chaos.
At that time, dinosaurs were not yet the overlords of the earth, and primitive fish had just been born.
Fossil horseshoe crabs found in 2008, 445 million years old
And as the gears of time turn, other animals become extinct and evolve.
Only the horseshoe crab has approached the catastrophe of the earth, and it has almost maintained the original appearance of hundreds of millions of years ago.
Therefore, some scientists call them "evolutionaryly sluggish taxa", which is what we call "living fossils".
However, in addition to the age and strange bones, the blue blood of the horseshoe crab is the biggest selling point.
It is this strange and strange blood that gives the race of horseshoe crabs the ability to survive for 400 million years with the ability to stand tall with other animals.
The common redness of blood is due to the fact that the vast majority of blood relies on iron-based hemoglobin to transport oxygen throughout the body.
When iron and oxygen are combined, they appear red that is visible to the naked eye.
But on the horseshoe crab, the iron is replaced by copper, and the color of copper oxidation is blue-green.
Therefore, in contrast to "hemoglobin", the respiratory protein of the horseshoe crab is figuratively called "hemocyanin".
Blood cells of horseshoe crabs
However, the most amazing thing about horseshoe's blood is not the color, but its unique antibacterial ability.
One of the most popular places to stay is by the sea.
But we know that the seaside is also an extremely dirty place, with about 1 billion bacteria in a gram of seafloor sediment.
Moreover, the horseshoe crab does not have layers of barriers like humans, and its blood circulation system is a relatively open pattern.
There is a large blood cavity in the body of the horseshoe crab, which is accessible in all directions, allowing direct contact between the blood and the tissue.
So as long as the bacteria drills into a certain slit in the shell of the horseshoe crab, it can easily travel unimpeded in the body of the horseshoe crab.
In addition, horseshoe crabs are arthropods and did not have white blood cells that could fight infection.
However, in order not to be swallowed by bacteria, the blood of the horseshoe crab has also evolved a protective mechanism different from that of humans.
Leukocyte phagocytosis
Although there are no white blood cells, the original horseshoe crab blood has a magical amoebic cell (with mobility).
When in contact with bacteria, amoeboid cells do not engulf the bacteria like white blood cells, but immediately atrophy and rupture.
The chemicals released in this way will cause the blood to coagulate locally, which can envelop harmful bacteria and block the spread of the disease.
It's just that the blue blood allows the horseshoe crab to escape the invasion of bacteria, but it also summons humans to catch it.
It can be said that "success is also blue blood, and defeat is also blue blood".
In 1956, fred bang was studying the blood circulation of the horseshoe crab when he discovered the strange death of a horseshoe crab.
The horseshoe crab, which was infected with the gram-negative bacteria on a large scale, had almost all of its blood clotted into a colloidal form.
Fred Bang
After several experiments, Bang finally discovered that it was an endotoxin* produced by bacteria that activated an enzyme in amoebic cells of the blood, causing the blood to coagulate.
Using this biospecificity of horseshoe's blood, he also developed a bacterial detector, the Limulus Amebocyte Lysate amoebas cell lysate.)
*Note: Bacterial toxins can be divided into two categories, exotoxin and endotoxin. Exotoxins are toxic substances secreted into the body of bacteria during the growth of bacteria, and the bacteria that produce exotoxins are mainly gram-positive bacteria, and some are gram-negative bacteria. The endotoxin, on the other hand, is a cell wall product of Gram-negative bacteria and exhibits toxicity only after the cells die.
This reagent is not only fast-reacting and extremely sensitive, but also can detect clues to the presence of bacteria.
Even if the concentration of bacterial endotoxins in the solution is only one part of a trillion, this blood extract can work to make the clear solution gelatinous.
If the sample is not contaminated with bacteria, blood clotting will not occur and can be judged as sterile.
In fact, bacteria have been threatening the safety of the human medical system.
Anything that enters the human body must be sterile, such as surgical implants, injections, or other treatment processes.
The sterility referred to here not only means that there are no live bacteria, but also requires the absence of pyrogens (endotoxins are the largest class of pyrogens).
Otherwise, patients are very prone to pyrogenic reactions, chills, fever, headache, vomiting, gray complexion, shock, and severe death.
However, bacteria are ubiquitous, so detection is particularly important.
If it is not used in the human body without bacterial testing, countless people will die from unhygienic injections.
Rabbit pyrogen detection
Before the invention of the horseshoe reagent, the "rabbit method" for detecting bacterial toxins was expensive and clumsy
The first is to inject a sample into the rabbit's body, and then ask the staff to check the rabbit's body temperature change every 30 minutes.
Although rabbits are sensitive to endotoxins, it takes at least 3 hours to determine the presence of bacterial endotoxins in the sample.
But now, we only need to add the reagent to the material under test and reverse it a few times to see the result from the presence or absence of coagulation.
Therefore, once the horseshoe reagent was introduced, it quickly replaced the inefficient rabbit detection method and became a big industry.
It can be widely used in endotoxin detection of injectable drugs, biological products, plasma products, anti-cancer drugs, etc.
In addition, in the clinic, the reagent is also suitable for rapid diagnosis of meningitis, cholera, plague, pertussis and other diseases caused by gram-negative bacteria, which is conducive to winning treatment time.
Therefore, each of us has been blessed by this blue-blooded creature.
Live blood collection site of horseshoe crabs
Because of its unique medical value, the blood of the horseshoe crab is also one of the most precious blood in the world.
The value of the blood of about 1 liter of horseshoe crab can be as high as $15,000, which is not inferior to gold.
Every year, 500,000 horseshoe crabs are brought into the laboratory to "donate blood" and contribute to human medicine.
First, the staff will bend the abdomen and tail of the horseshoe crab to fix it.
The pericardium is then pierced with a steel needle and about 30% of the total blood volume is removed.
This blood collection process takes about one to three days, and the horseshoe crabs return to normal before being released into the sea.
Although it is not counted as killing chickens to retrieve eggs, different data show that 10% to 30% of horseshoe crabs will die after blood collection.
So this means that more than 50,000 horseshoe crabs still die in "blood donation" every year.
In addition, after blood collection, the horseshoe crab will also lose vitality and move slowly.
Compared with other peers who had not taken blood, the experimented horseshoe crabs also became insensitive to tides, with a decreased mating probability and a sharp decrease in spawning.
Fortunately, scientists are not indifferent to this problem.
After more than a decade since the 1980s, the world's first non-horseshoe blood test kit was finally launched in 2003.
Although it is still difficult to walk on the road of commercial promotion, more and more pharmaceutical companies have joined the ranks.
Perhaps in the near future, the "forced blood donation" activity of the horseshoe crab will slowly disappear.
But even if pharmaceutical companies no longer need the blue blood of the horseshoe crab, will they be able to escape their tragic fate? The answer may be no.
At least from the past to the present, the horseshoe crab has never received preferential treatment from humans.
As early as the colonial period in the United States, people used "horseshoe fat" to fatten the land.
Millions of horseshoe crabs are caught and crushed into fertilizer, and in some cases become pig feed.
Later, fishermen also discovered that it was possible to catch conchs with horseshoe crabs as bait.
So from the 90s, they suffered again, and the number of catches went up again.
Horseshoe manure
In China, the fate of the horseshoe crab is not much better.
The deterioration of habitat and human overfishing have caused the Chinese horseshoe crab population to fall into a large number of declines.
In the 1980s, when the reagent was first introduced to China, the reagent factory sprung up like a mushroom.
Market demand has also led to the capture of large quantities of Chinese horseshoe crabs.
However, in the environment of irregular blood collection and insufficient protection, a large number of horseshoe crabs eventually went to death.
In addition, most horseshoe crabs are squeezed out of surplus value by "doing their best" after blood is taken.
They are not released into the ocean, but instead use the carcasses of the horseshoe crabs for composting or selling as ingredients.
After a long follow-up survey, the researchers found that the population of Chinese horseshoe crabs in China's Beibu Gulf has declined by 90% in the past 20 years.
Friends who grew up by the sea should have a deeper understanding.
Over the years, the price of horseshoe crab has doubled many times.
From the cheap in the past to the seafood that no one wants to eat, it has suddenly become a precious "mountain treasure seafood".
But in fact, the horseshoe crab is really not a human delicacy.
It itself has less meat, and the meat is hard and woody, and the umami taste is insufficient and the fishy taste is extremely heavy.
I have seen some people describe it as "even the urine discharged in the days after eating is fishy".
If you do not go through a variety of complex processing spices, such as making Chaoshan crab, it is difficult for ordinary people to enter.
In the original words of the gourmand Cai Lan, it is "a pity to abandon it, but it is tasteless to eat".
The production of horseshoe, the rice beads of the horseshoe need to be cooked and fried, the crab meat is marinated and sun-dried, in order to make a horseshoe sauce, these horseshoe sauce is the main material for making the horseshoe
In addition, crab meat has a macromolecular non-specific protein sensitizing substance.
Eating horseshoe crabs can cause allergic rashes, redness, and itching on the skin, and in severe cases, it can lead to anaphylactic shock or fatal toxic reactions, and the mortality rate of poisoning is higher.
The round-tailed horseshoe crab, which is very similar in appearance to the Chinese horseshoe crab, is even more inedible, and the tetrodotoxin in its body kills the gluttonous in minutes.
A is a round-tailed horseshoe crab and E is a Chinese horseshoe crab
However, because resources have become scarce, Chinese horseshoe crab has become morbidly popular in the food market.
In fact, don't just think about eating, the value of the horseshoe crab itself may be far beyond human imagination.
In addition to the reagents for horseshoe crabs that benefit all people, a study on horseshoe crabs has won the Nobel Prize as early as the last century.
There are many small eyes on the compound eyes of the horseshoe crab
The horseshoe crab has four eyes, and its compound eyes are composed of 800-1000 relatively independent small eyes.
The nerve cells in the eyes of the horseshoe crab are also the most easily obtained, so they have always been an important object of retinal physiology research.
The famous physiologist Hartline (Haldan Keffer) discovered the phenomenon of "side inhibition" through the eyes of the horseshoe crab:
When the illumination area expands from a small eye to a nearby small eye, the electrical pulse emitted by the previous small eye
Instead of increasing, the intensity decreases.
In other words, when a small eye is stimulated by light, the small eyes around it are inhibited.
In the "side suppression" illusion diagram, the color at AB is actually the same
Side suppression illusion diagram, which is a static diagram with only white dots
With this side suppression, the eye can enhance the edge contrast of the image, omit detail to highlight the contour, and make the subjective field of view clearer.
Based on this discovery, Hartland also received the 1967 Nobel Prize in Physiology or Medicine.
This principle of "side suppression", which also provided inspiration for contemporary biomimicry, was applied to television and radar systems, greatly improving imaging clarity and sensitivity.
Horseshoe crabs can survive hundreds of millions of years of earth wind and frost, and there must be two brushes.
Leaving aside for the time being the possibility of crossing the river and demolishing the bridge, it is still unknown whether human beings can study it thoroughly and truly "squeeze out" the value.
And blindly framing the value of a species to death on "eating" is not too far-sighted.
*References
The History of Limulus and Endotoxin.NC State University
The Blood Harvest.The Atlantic.2014.02.26
Also the horseshoe crab, why is the Chinese horseshoe crab endangered?
CHEN Zhangbo,FAN Hangqing,LIAO Yongyan,QIU Guanglong,XIE Huilian,LIN Wuying. A living fossil of an animal facing a dilemma of survival, the horseshoe crab. Science[J].2015.05