Without viruses, there would be no humans and no other species. The word "virus" always brings to mind the horror of death brought about by invisible shadows.

In fact, viruses infect all living things - not just humans - and many of them do not cause disease at all. Viruses are part of the course of life on Earth, and what role they have played in the evolution of life on Earth is still a mystery, but one that is slowly being solved.

A virus can infect all forms of life; in addition to plants and animals, it infects bacteria, archaea, and even viruses themselves. Viruses are everywhere, and in staggering numbers - 10 million viruses per milliliter of seawater.

Viruses, too, seem to be a commonplace concept in our daily lives, but if you ask virologists, "virus" itself is not so well defined at all

For more than 100 years, virologists have been thinking about how to give a watertight definition of a virus. But every time they think they may have found a suitable definition, there is always a newly discovered virus that does not fit the definition.

It would be a huge misunderstanding of viruses to think that this ubiquitous virus is only associated with causing disease. In fact, translating VIRUS as "virus" is a huge misunderstanding, because many VIRUS are not only not "virulent" but also beneficial to humans and other organisms.

There is actually a very delicate ecological balance between viruses and their hosts. Many viruses are non-pathogenic, and the vast majority of viruses may be symbiotic with their hosts, that is, they get what they need from the host without causing harm to the host. Some viruses are mutually beneficial to their hosts, giving them the benefits they need to survive while also profiting from them.

Severe illness or death indicates that the virus-host relationship is still in the early stages of a mutual game. Over time, viruses generally evolve to become less lethal.

There are various feuds between humans and viruses. When you learn about viruses, you learn that without viruses, there would be no humans, and no other species.

Science and nature seem to play a constant game of cat and mouse. Viruses are simpler and lesser than humans. Yet existence is justified, and like humans, they seem to be born with the ability to survive in this world and to be extremely adaptable. Thus, the development and vaccination of influenza vaccines is like a never-ending chase, because influenza viruses can keep mutating, and eventually there will always be some mutant strains that can successfully resist the currently available vaccines. It is perhaps reassuring, however, that the virus does not generally "kill" its hosts as easily, since doing so would also eliminate its means of reproduction and perpetuation as a species.

An optical microscope image is an image generated by a conventional light microscope. The light microscope is a traditional microscope invented in the 16th century that magnifies a specimen through a lens in natural or artificial light. When light hits an object, the light is reflected differently depending on the condition of the object such as color, texture and angle. And this reflected light enters our eyes or (in some cases) passes through the lens again into our eyeball and produces a stimulus signal on the photoreceptor cells of the retina.

In the late 17th century, the microscope became an important tool for scientific research. The microscope is the simplest low-tech, low-cost tool for observing microscopic things. The nature of the microscope has changed very little in the 400 years since it was invented.

In the early 20th century, scientists developed a new, highly technical microscope to replace the traditional light microscope. The first electron microscope was introduced in the 1930s, and instead of using a light beam, it used a stream of electrons from an electron gun to "illuminate" the target. While conventional microscopes use a lens to change the direction of light propagation, electron microscopes use electromagnets to change the direction of the electron beam.