the idea that all living cells come from preexisting living cells was proposed by hershel mitchell.
the idea that all living cells come from preexisting living cells was proposed by hershel mitchell.
the idea that all living cells come from preexisting living cells was proposed by?
hershel mitchell
cells, which were once invisible to the naked eye, were first seen in 17th century europe with the invention of the compound microscope. robert hooke was the first person to term the building block of all living organisms as "cells" after looking at cork. the cell theory states that all living things are made up of cells. the theory also states that both plants and animals are composed of cells which was confirmed by plant scientist, matthias schleiden and animal scientist, theodor schwann in 1839. 19 years later, rudolf virchow contributed to the cell theory, arguing that all cells come from the division of preexisting cells. in recent years, there have been many studies which question the cell theory. scientists have struggled to decide whether viruses are alive or not. viruses lack common characteristics of a living cell, such as membranes, cell organelles, and the ability to reproduce by themselves. viruses range from 0.005 to 0.03 micrometers in size whereas bacteria range from 1-5 micrometers. modern day cell biology research looks at different ways to culture and manipulate cells outside of a living body to further research in human anatomy and physiology, to derive treatments and other medications, etc. the techniques by which cells are studied have evolved. advancement in microscopic techniques and technology such as fluorescence microscopy, phase-contrast microscopy, dark field microscopy, confocal microscopy, cytometry, transmission electron microscopy, etc. have allowed scientists to get a better idea of the structure of cells.
cell biology
a vital stain in a casual usage may mean a stain that can be applied on living cells without killing them. vital stains have been useful for diagnostic and surgical techniques in a variety of medical specialties. in supravital staining, living cells have been removed from an organism, whereas intravital staining is done by injecting or otherwise introducing the stain into the body. the term vital stain is used by some authors to refer to an intravital stain, and by others interchangeably with a supravital stain, the core concept being that the cell being examined is still alive. in a more strict sense, the term vital staining has a meaning contrasting with supravital staining. while in supravital staining the living cells take up the stain, in "vital staining" – the most accepted but apparently paradoxical meaning of this term, the living cells exclude the stain i.e. stain negatively and only the dead cells stain positively and thus viability can be assessed by counting the percentage of total cells that stain negatively. very bulky or highly charged stains that don't cross live plasma membrane are used as vital stains and supravital stains are those that are either small or are pumped actively into live cells. since supravital and intravital nature of the staining depends on the dye, a combination of supravital and vital dyes can also be used in a sophisticated way to better classify cells into distinct subsets (e.g. viable, dead, dying etc.).
vital stain