Precipitins 1930 Bio-Cinema (Patreon)

more at http://quickfound.net/

Silent, with title cards. 'Identification of human vs. animal blood, stains through chemical tests - scientists, labs, chemists, rabbits, experiments, blood, nurses, lab technicians, microscopes, test tubes, etc...'

Originally a public domain film from the Library of Congress Prelinger Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.

The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).

https://en.wikipedia.org/wiki/Precipitin

Wikipedia license: http://creativecommons.org/licenses/by-sa/3.0/

A precipitin is an antibody which can precipitate out of a solution upon antigen binding.

Precipitin reaction

The precipitin reaction provided the first quantitative assay for antibody. The precipitin reaction is based upon the interaction of antigen with antibody leading to the production of antigen-antibody complexes.

To produce a precipitin reaction, varying amounts of soluble antigen are added to a fixed amount of serum containing antibody. As the amount of antigen added:

In the zone of antibody excess, each molecule of antigen is bound extensively by antibody and crosslinked to other molecules of antigen. The average size of antibody-antigen complex is small; cross-linking between antigen molecules by antibody is rare.

In the zone of equivalence, the formation of precipitin complexes is optimal. Extensive lattices of antigen and antibody are formed by cross-linking.

At high concentrations of antigen, the average size of antibody-antigen complexes is once again small because few antibody molecules are available to cross-link antigen molecules together.

The small, soluble immune complexes formed in vivo in the zone of antigen excess can cause a variety of pathological syndromes.

Antibody can only precipitate antigenic substrates that are multivalent—that is, only antigens that have multiple antibody-binding sites epitopes. This allows for the formation of large antigen:antibody complexes...

https://en.wikipedia.org/wiki/Antibody

An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein produced mainly by plasma cells that is used by the immune system to neutralize pathogens such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the pathogen, called an antigen, via the fragment antigen-binding (Fab) variable region. Each tip of the "Y" of an antibody contains a paratope (analogous to a lock) that is specific for one particular epitope (analogous to a key) on an antigen, allowing these two structures to bind together with precision. Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system, or can neutralize its target directly (for example, by inhibiting a part of a microbe that is essential for its invasion and survival). Depending on the antigen, the binding may impede the biological process causing the disease or may activate macrophages to destroy the foreign substance...

Antibodies are secreted by B cells of the adaptive immune system, mostly by differentiated B cells called plasma cells. Antibodies can occur in two physical forms, a soluble form that is secreted from the cell to be free in the blood plasma, and a membrane-bound form that is attached to the surface of a B cell and is referred to as the B-cell receptor (BCR). The BCR is found only on the surface of B cells and facilitates the activation of these cells and their subsequent differentiation into either antibody factories called plasma cells or memory B cells that will survive in the body and remember that same antigen so the B cells can respond faster upon future exposure. In most cases, interaction of the B cell with a T helper cell is necessary to produce full activation of the B cell and, therefore, antibody generation following antigen binding. Soluble antibodies are released into the blood and tissue fluids, as well as many secretions to continue to survey for invading microorganisms...

Though the general structure of all antibodies is very similar, a small region at the tip of the protein is extremely variable, allowing millions of antibodies with slightly different tip structures, or antigen-binding sites, to exist. This region is known as the hypervariable region. Each of these variants can bind to a different antigen. This enormous diversity of antibody paratopes on the antigen-binding fragments allows the immune system to recognize an equally wide variety of antigens...