Wikipedia:Reference desk/Archives/Science/2023 April 11

= April 11 =

Egg White and Egg Yolk
The egg white becomes feathers and egg yolk becomes body of a bird. If you break the egg looking at the egg yolk all looks same. Now how does the similar part takes the form of different body parts. I have seen videos how it happens. But how is it decided inside egg that which part of egg yolk will take the form of a body part.

https://en.wikipedia.org/wiki/Bird_anatomy Lucidsonsf (talk) 14:29, 11 April 2023 (UTC)
 * Your question starts with a false premise. When you say The egg white becomes feathers and egg yolk becomes body of a bird, I'm not sure where you read that, but it's completely wrong.  Yolk doesn't "become" any part of the bird, it just acts as a nutrient source to provide energy growing embryo.  Egg white, the clear-ish part between the yolk and the shell, serves also to provide some nutrition to the embryo (mainly in the form of protein, i.e. as a source of amino acids so the bird embryo has the components necessary to build itself) and also to help protect the fragile embryo, acting as a sort of "padding" and "shock absorber" for the embryo.  The Wikipedia article Bird egg contains more information about the structure; incidentally, neither the yolk or egg white is strictly the embryo, the embryo itself begins as a single fertilized ovum, which is a microscopic single cell, and too small to see in an unfertilized egg, and will grow through the same stages that all embryos undergo.  The ovum when fertilized will form the embryo, which attaches to the outside of the yolk membrane via a structure known as the amnion, which allows the embryo to access the energy source provided by the yolk.  -- Jayron 32 14:53, 11 April 2023 (UTC)
 * Topic adjacent, but in trying to make sense of this question, I did come upon the fact that feathers contain a large amount of disulfide cross-links in their β-keratin, and egg white does contain roughly twice the sulfur content as egg yolk. I wonder if that is the source of this idea, that there is (at least potentially) more useful material for feathers in egg white than in egg yolk? Of course, feathers aren't the only parts of a bird that need cysteine or methionine amino acids (and so sulfur in the white will end up in the embryo body), and just because the white has a higher sulfur content than the yolk in no way means that none of the sulfur in the yolk will end up in the feathers. I wonder if anyone has done any isotopic labeling experiments with isotopes of sulfur in egg white and egg yolk to track that metabolic pathway (likely showing that, assuming it is bioavailable, it just goes to wherever it is currently needed in the embryonic development no matter whether it comes from white or yolk)? -- OuroborosCobra (talk) 15:12, 11 April 2023 (UTC)
 * (edit conflict) Well, first, I'm not sure that your initial claim is even true. I don't think I've seen anywhere evidence that the egg white becomes feathers and yolk the body. However, in terms of how the nutrients of the yolk become different parts of the growing bird embryo, consider 'anything that you eat, ever. When you eat a steak, how does that material become parts of neurons or liver cells or skin cells? Your body digests the nutrient material and distributes it as needed. An avian embryo is using the yolk as a source of nutrients during growth inside of the egg in much the same way, distributing them as needed, and then going through various processes such as translation in ribosomes to make proteins according to genetic information that the ribosomes receive following transcription. That is an oversimplification, of course, but it gets the general idea across. Egg whites also contain nutrients, including albumin, which are similarly used by the embryo, probably after some form of digestion to break them down into amino acids that are then used in translation to make new proteins. They do not physically become the feathers anymore than any other material useful for feather making in the yolk. Feathers, for example, contain many disulfide bridges in their β-keratin proteins, which means they need the amino acid cysteine. This can either be scavenged from their diet by digesting proteins to get single amino acid residues, or it can be synthesized within the body, though that still requires starting material contained within accessible nutrients, such as sulfur in a useful form. Sulfur can be found in both the egg white and in the egg yolk, and the bird embryo doesn't care which it is coming from. A sulfur atom in a yolk isn't any different than a sulfur atom in the egg white. While it is true that sulfur is more abundant in the egg white than the egg yolk, feathers are not the only structure in a bird that has disulfide bridges, and so that egg white material will also make its way into the bird embryo body. --OuroborosCobra (talk) 15:05, 11 April 2023 (UTC)
 * More simply put: yolk and egg white are made of the same building blocks (atoms and molecules) that also make up feathers and bones and skin and other body parts. The various body parts don't get "made" from specifically the yolk or egg white; it's akin to having a giant pile of Lego to build things out of.  When you digest materials, you're just adding bricks to your pile of Lego, and when you build something new like a feather or skin or an enzyme, you just pull what you need from the giant pile of Lego.  It doesn't really matter where the bricks in the Lego came from at a biochemical level... It's all just a reservoir of atoms and molecules, and those atoms and molecules aren't really distinguishable as to where they came from.  Methionine is identical wherever it came from, as is Sulfur as is any of the other atoms and/or molecules that any living thing is processing billions of times every second.  -- Jayron 32 16:11, 11 April 2023 (UTC)
 * If you read up on human embryonic development, a lot of that is applicable to birds as well, because developmental pathways are highly conserved especially among chordates. See also evolutionary developmental biology. Neat fact: birds even still have the genes to make teeth; the genes just aren't "turned on", so they don't produce them. Scientists have been able to switch them back on in embyros with genetic manipulation techniques. --47.155.46.15 (talk) 21:58, 13 April 2023 (UTC)

Transfer technology in 1913
I have just come across this YouTube video of GWR Star class locomotive 4041 Prince of Wales being built at Swindon Works in 1913. From 4:26 to 5:19, a man is shown applying the lettering and coat of arms to the tender, using what looks like a self-adhesive transfer of some sort. I presume that this allowed a printed (or painted?) design to be pre-created more conveniently than having to paint it on a vertical surface in a locomotive works.

According to Decal, this sort of process was invented in the 1700's, but it gives no clue as to the materials used before the development of vinyl and other plastics. What sort of materials or techniques were available to locomotive builders in 1913 ? -- Verbarson talkedits 22:24, 11 April 2023 (UTC)
 * The decalcomania article mentioned in the lead of the decal article says tracing paper, glass, also I see waxed paper mentioned when googling. I wonder if glassine is meant instead of glass. Abductive  (reasoning) 05:39, 12 April 2023 (UTC)
 * A sheet of glass can easily be pressed together with a pliable surface such as a canvas. --Lambiam 06:13, 12 April 2023 (UTC)
 * The paint is on a transfer sheet, then it is pressed onto the receiving surface. Then the paint is somehow induced to stay on the receiving surface, then the transfer sheet is removed. If the transfer sheet is glass, how would you press it onto a surface without breaking it? How would you get the paint to leave the glass and stick to the receiving surface? How would you pull away the glass? I think it is much more likely that various kinds of paper were used, the common thread between them being that they were translucent so people could see what they were doing, you know, not apply the decal upside-down. Then the paper could be peeled off, or washed away with water. Abductive  (reasoning) 06:34, 12 April 2023 (UTC)
 * You lay the glass on a flat surface with the paint-bearing side up, put the canvas over it, and apply pressure. Some of the paint will stick to the canvas, enough to transfer the image. --Lambiam 13:32, 12 April 2023 (UTC)
 * And this was used as a method in 1913? Abductive  (reasoning) 02:26, 13 April 2023 (UTC)
 * The 18th century origin of the process is attributed to Simon François Ravenet, who called his process décalquer, which is the derivation of the term Decalcomania and later "decal". This process involved the transfer of ceramic pigments onto tissue paper using metal plates as with a printing press and mass produced.  This then can be lifted from the paper using water (as with a modern decal) and transferred onto pottery and fired.  See also: Transfer printing.  I don't know if this type of ceramic print transfer was used on metal objects such as a locomotive, but can see no reason why it couldn't have been -- as in a form of printed vitreous enamel? --136.56.52.157 (talk) 06:02, 12 April 2023 (UTC) . . . See also: Industrial porcelain enamel
 * In the video, the transfer medium is peeled off (hence it seems to be paper or cloth) and the decal is rubbed down, apparently with bare hands (hence it is dry, and fairly robust, as it does not smudge or tear). I assume that the bare surface it is applied to is paint, or possibly varnish. The whole surface, including the decals, may have been varnished again afterwards, for better protection from wind and weather. -- Verbarson talkedits 08:07, 12 April 2023 (UTC)
 * See also Transfer printing where "Apart from pottery, the technique was used on metal, ...". Transfer printing was used on an industrial scale from the 1750s onwards in England.  Although developed for ceramic decoration, it was also used on wood and metal.  It's worth noting that the transfers are seen being used for the words "Great Western" and the company crest.  These would be applied to all locos, and would be worth printing. Martin of Sheffield (talk) 09:13, 12 April 2023 (UTC)
 * Transfer printing involves ink or pigment. In the video, the decal is more robust than just liquid or powder, it is given no time to dry, nor is it baked on afterwards. -- Verbarson talkedits 15:59, 12 April 2023 (UTC)
 * I was randomly reading this only yesterday: SR West Country and Battle of Britain classes, but these enamelled crests may only apply to Southern Railway locos. By the way, the Swindon Works is now the Swindon Designer Outlet and you can still see some of the overhead gantries and pulleys as you browse for your overpriced remaindered tat. MinorProphet (talk) 19:52, 12 April 2023 (UTC)
 * I just now watched the video. It does look like a typical decal was applied using water.  Cellophane was available in 1913, so it could have been simply a decal printed on cellophane. --136.56.52.157 (talk) 04:47, 13 April 2023 (UTC)
 * Cellophane was not patented until 1912; I'm not sure a traditional company like the GWR would be using such new-fangled stuff on their top-of-the-line locos, in a fairly tough environment. (But I have no proof; feel free to prove me wrong!) -- Verbarson talkedits 09:57, 13 April 2023 (UTC)
 * I couldn't verify, but the railroad industry was considered high-tech in its day, and it could be that "new-fangled" decals were considered "ultra-modern". To this day, metal decals with cellophane backing are used on aircraft. --136.56.52.157 (talk) 12:29, 13 April 2023 (UTC)
 * I couldn't verify, but the railroad industry was considered high-tech in its day, and it could be that "new-fangled" decals were considered "ultra-modern". To this day, metal decals with cellophane backing are used on aircraft. --136.56.52.157 (talk) 12:29, 13 April 2023 (UTC)