Apr 202018
 

On this date in 1862, Louis Pasteur (and colleagues) concluded and published a series of experiments that definitively refuted the theory of spontaneous generation: the notion that living organisms can be generated by inanimate substances. Spontaneous generation was the dominant theory for thousands of years, and it’s not hard to understand why. When I tried to germinate avocado seeds in water in Myanmar for a school project, I had to dump the water constantly because every few days you could see mosquito larvae swimming in it. Where did they come from? Rotting meat frequently breeds maggots; old fruit seems to generate fruit flies. You need a good microscope, and controlled experiments, to figure out that living things are generated only by living things that are alike. Pasteur settled the matter, although there were holdouts for a while.

In the 6th and 5th centuries BCE, Greek philosophers, called physiologoi (φυσιολόγοι) that is, investigators of “nature” (φυσις – from which we get “physics”), attempted to give natural explanations of phenomena that had previously been ascribed to the agency of the gods. The physiologoi sought the material principle or arche (ἀρχή) of things, emphasizing the rational unity of the external world and rejecting theological or supernatural explanations. Anaximander, who believed that all things arose from the elemental nature of the universe, the apeiron (ἄπειρον) or the “unbounded” or “infinite,” was likely the first Western thinker to propose that life developed spontaneously from nonliving matter. The primal chaos of the apeiron, eternally in motion, served as a substratum in which elemental opposites (e.g., wet and dry, hot and cold) generated and shaped the many and varied things in the world. According to Hippolytus of Rome in the 3rd century CE, Anaximander claimed that fish or fish-like creatures were first formed in the “wet” when acted on by the heat of the sun and that these aquatic creatures gave rise to human beings. Censorinus, writing in the 3rd century, reports:

Anaximander of Miletus considered that from warmed up water and earth emerged either fish or entirely fishlike animals. Inside these animals, men took form and embryos were held prisoners until puberty; only then, after these animals burst open, could men and women come out, now able to feed themselves.

Anaximenes, a pupil of Anaximander, thought that air was the element that imparted life and endowed creatures with motion and thought. He proposed that plants and animals, including human beings, arose from a primordial terrestrial slime, a mixture of earth and water, combined with the sun’s heat. Anaxagoras, too, believed that life emerged from a terrestrial slime. However, he held that the seeds of plants existed in the air from the beginning, and those of animals in the aether. Xenophanes traced the origin of man back to the transitional period between the fluid stage of the earth and the formation of land, under the influence of the sun.

In what has occasionally been seen as a prefiguration of a concept of natural selection, Empedocles accepted the spontaneous generation of life but held that different forms, made up of differing combinations of parts, spontaneously arose as though by trial and error: successful combinations formed the species we now see, whereas unsuccessful forms failed to reproduce.

Aristotle proposed that in sexual reproduction, the child inherits form (eidos) from the father and matter from the mother, as well as πνεῦμα (pneuma) – breath, life, or spirit – either from the father or from the environment. In spontaneous generation, the environment could effectively replace the parents’ contributions of form, matter, and pneuma:

Now there is one property that animals are found to have in common with plants. For some plants are generated from the seed of plants, whilst other plants are self-generated through the formation of some elemental principle similar to a seed; and of these latter plants some derive their nutriment from the ground, whilst others grow inside other plants … So with animals, some spring from parent animals according to their kind, whilst others grow spontaneously and not from kindred stock; and of these instances of spontaneous generation some come from putrefying earth or vegetable matter, as is the case with a number of insects, while others are spontaneously generated in the inside of animals out of the secretions of their several organs.

(History of Animals, Book V, Part 1)

I first came across this notion when I studied Virgil’s Georgics, Book IV, on bee keeping. Virgil advises the following, if a bee keeper loses his stock:

First they choose a narrow place, small enough for this purpose:
they enclose it with a confined roof of tiles, walls close together,
and add four slanting window lights facing the four winds.

Then they search out a bullock, just jutting his horns out
of a two-year-old’s forehead: the breath from both its nostrils
and its mouth is stifled despite its struggles: it’s beaten to death,
and its flesh pounded to a pulp through the intact hide.

They leave it lying like this in prison, and strew broken branches
under its flanks, thyme and fresh rosemary.
This is done when the Westerlies begin to stir the waves
before the meadows brighten with their new colours,
before the twittering swallow hangs her nest from the eaves.

Meanwhile the moisture, warming in the softened bone, ferments,
and creatures, of a type marvelous to see, swarm together,
without feet at first, but soon with whirring wings as well,
and more and more try the clear air, until they burst out,
like rain pouring from summer clouds,
or arrows from the twanging bows,
whenever the lightly-armed Parthians first join battle.

Spontaneous generation is discussed as a fact in literature well into the Renaissance. Shakespeare says snakes and crocodiles form from the mud of the Nile:

Your serpent of Egypt is bred now of your mud by the operation of your sun. So is your crocodile.  

(Anthony and Cleopatra Act 2 scene 7)

Izaak Walton agrees when he says that eels “as rats and mice, and many other living creatures, are bred in Egypt, by the sun’s heat when it shines upon the overflowing of the river.”

Jan Baptist van Helmont (1580–1644) used experimental techniques, such as growing a willow for five years and showing it increased mass while the soil showed a trivial decrease in comparison. He attributed the increase of mass to the absorption of water. His notes also describe a recipe for mice (a piece of soiled cloth plus wheat for 21 days) and scorpions (basil, placed between two bricks and left in sunlight). His notes suggest he may even have tried these things.

The ancient beliefs were subjected to testing starting in the 17th century. In 1668, Francesco Redi challenged the idea that maggots arose spontaneously from rotting meat. In the first major experiment to challenge spontaneous generation, he placed meat in a variety of sealed, open, and partially covered containers. Realizing that the sealed containers were deprived of air, he used “fine Naples veil”, and observed no worm on the meat, but they appeared on the cloth. Redi used his experiments to support the preexistence theory put forth by the Church at that time, which maintained that living things originated from parents. Pier Antonio Micheli, around 1729, observed that when fungal spores were placed on slices of melon the same type of fungi were produced that the spores came from, and from this observation he noted that fungi did not arise from spontaneous generation.

In 1745, John Needham performed a series of experiments on boiled broths. Believing that boiling would kill all living things, he showed that when sealed right after boiling, the broths would cloud, allowing the belief in spontaneous generation to persist. His studies were rigorously scrutinized by his peers and many of them agreed.

Lazzaro Spallanzani modified the Needham experiment in 1768, attempting to exclude the possibility of introducing a contaminating factor between boiling and sealing. His technique involved boiling the broth in a sealed container with the air partially evacuated to prevent explosions. Although he did not see growth, the exclusion of air left the question of whether air was an essential factor in spontaneous generation. However, by that time there was already widespread skepticism among major scientists, to the principle of spontaneous generation. Observation was increasingly demonstrating that whenever there was sufficiently careful investigation of mechanisms of biological reproduction, it was plain that processes involved basing of new structures on existing complex structures, rather from chaotic muds or dead materials.

Louis Pasteur’s 1859 experiment is widely seen as having settled the question of spontaneous generation. He boiled a meat broth in a flask that he invented called the swan-necked flask (because ithad a long neck that curved downward, like that of a swan). The idea was that the bend in the neck prevented falling particles from reaching the broth, while still allowing the free flow of air. The flask remained free of growth for an extended period. When the flask was turned so that particles could fall down the bends, the broth quickly became clouded. A flask in which broth was boiled and immediately exposed to air, became clouded quickly. Minority objections to the conclusiveness of the experiments were persistent, however, and subsequent, more rigorous, experiments were needed to bring the question to an end for the die-hards. Hey – we still have flat earthers.

The obvious ingredient for today’s celebratory recipe is Lyle’s golden syrup. The label has the ancient slogan on it, “Out of the strong came forth sweetness,” a reference to a riddle put by Samson in Judges 14:14, the answer to which is that dead lions propagate honey bees. Here is the recipe for treacle tart taken from the Lyle’s website (unedited):

https://www.lylesgoldensyrup.com/recipe/lovely-treacle-tart

Lyle’s Treacle Tart

INGREDIENTS

FOR THE PASTRY

295g Plain flour, plus extra for dusting
165g Unsalted butter (chilled + cubed)
4½ tbsp Cold water
Pinch of salt

FOR THE FILLING

450g Lyle’s Golden Syrup
25g Unsalted butter
1 Large egg
3 tbsp Double cream
2 sachets Dr Oetker Lemon Ready Zest
30g breadcrumbs (increase to 80g for a denser mixture)
Crème fraîche, for serving

Instructions

Pulse the flour, butter and salt in a blender until the mixture resembles large crumbs. Add the water and briefly blend until it comes together in a ball – then wrap in cling film and chill for 20 minutes.

Cut off one-third of the pastry and set aside for the lattice top. Roll the rest of pastry out on a lightly floured surface to about 4cm (1½”) bigger than a loose-bottomed tart tin, 22cm (9”) x 3.5cm (1½”) deep. Line the tin with pastry, trim the excess and lightly prick with a fork, then chill for 30 minutes. Add the excess to the pastry set aside for the lattice top.

Preheat the oven to 190°C/170° Fan, 375°F, Gas 5. Lay some baking parchment in the tin over the pastry and then put your baking beans in, over the parchment. Place in the oven and pre-bake for 15 minutes on the middle shelf. Remove the paper and beans and bake for a further 8-10 minutes to dry the pastry out. Remove the tart from the oven and put it on a baking tray. Reduce the oven temperature down to 180°C/160°Fan, 350°F, Gas 4, ready for later.

Roll the extra lattice top pastry out thinly and set aside on a tray to chill in the fridge for about 20-30 minutes – this makes it easier to handle.

Gently warm the Lyle’s Golden Syrup in a pan over a low heat, remove, then add the butter and stir until melted. Leave to cool a little. Using a fork, beat the egg and cream together in a separate bowl, then quickly beat in the syrup mixture along with the lemon zest and crumbs. Pour into the pastry case.

Remove the pastry from the fridge and cut into 10 strips of 1cm width which are long to overhang the edges of the tart tin.

Lay 5 parallel strips equally spaced over the tart. Fold back every other strip and place one strip of dough perpendicular to the parallel strips. Unfold the folded strips over the perpendicular strip. Now take the parallel strips that are running underneath the perpendicular strip and fold them back over. Lay down a second perpendicular strip (evenly spaced) and unfold the folded parallel strips.

Continue this process until all 10 strips have been placed. Trim the edges of the strips for a neat finish to fit inside the tart.

Bake on the middle shelf for 45-50 minutes until richly brown and set. (The filling will still be a bit wobbly but it will firm up on cooling.) Remove, leave to cool until warm, then remove from the tin, slide onto a plate and serve.

Nov 202013
 

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Today is the birthday (1886) of Karl Ritter von Frisch, Austrian ethologist and entomologist who received the Nobel Prize in Physiology or Medicine in 1973, along with Nikolaas Tinbergen and Konrad Lorenz. His work centered on investigations of the sensory perceptions of the honey bee and he was one of the first researchers to translate the meaning of the honey bee “waggle dance,” a highly sophisticated method bees use to communicate the location of food sources to the hive.  His findings were largely dismissed or disputed when first published, but have since been confirmed.

Karl von Frisch was the son of the surgeon and urologist Anton Ritter von Frisch (1849-1917) and his wife Marie, née Exner. He was the youngest of four sons, all of whom became university professors. He studied in Vienna under Hans Leo Przibram, and in Munich under Richard von Hertwig, initially in the field of medicine but later turning to the natural sciences. He received his doctorate in 1910 and in the same year started work as an assistant in the zoology department of Munich University. In 1912 he became a lecturer in zoology and comparative anatomy there; and in 1919 was promoted to a professorship. His research on honeybees was continued by his student Ingeborg Beling. In 1921 he went to Rostock University as a professor of zoology and director of an institute. In 1923 he accepted the offer of a chair at Breslau University, returning in 1925 to Munich University, where he became the head of the institute of zoology.

In 1933 the Nazi regime passed the Civil Service Law requiring all public servants to provide proof of Aryan ancestry. Von Frisch was unable to account for the ancestry of one of his grandparents and was therefore classified as a mischling of ?th Jewish ancestry, but formally allowed to keep his job. However groups of students and lecturers worked to have him dismissed from the university, preferring a committed National Socialist. Frisch also attracted negative attention for employing Jewish assistants, including many women, and for practicing “Jewish science.” Eventually Frisch was forced into retirement, but the decision was reversed due to advances in his research on combating nosema infections in bees and his forced retirement was postponed until after the war. Frisch also worked actively to help Polish scientists who had been singled out for internment by Gestapo.

After the institute of zoology was destroyed in World War II, he went to the University of Graz in 1946, remaining there until 1950 when he returned to the Munich institute after it was reopened. He retired in 1958 but continued his research. Karl von Frisch married Margarete, née Mohr. Their son, Otto von Frisch, was director of the Braunschweig natural history museum between 1977 and 1995.

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Von Frisch’s study of honeybee sensory perception was all-encompassing:

Sense of smell: Frisch discovered that bees can distinguish various blossoming plants by their scent, and that each bee is “flower constant.” Surprisingly, their sensitivity to a “sweet” taste is only slightly stronger than in humans. He thought it possible that a bee’s spatial sense of smell arises from the firm coupling of its olfactory sense with its tactile sense.

Optical perception: Frisch was the first to demonstrate that honey bees had color vision, which he accomplished by using classical conditioning. He trained bees to feed on a dish of sugar water set on a colored card. He then set the colored card in the middle of a set of gray-toned cards. If the bees see the colored card as a shade of gray, then they will confuse the blue card with at least one of the gray-toned cards; bees arriving to feed will visit more than one card in the array. On the other hand, if they have color vision, then the bees visit only the blue card, as it is visually distinct from the other cards. A bee’s color perception is comparable to that of humans, but with a shift away from the red toward the ultraviolet part of the spectrum. For that reason bees cannot distinguish red from black (colorless), but they can distinguish the colors white, yellow, blue and violet. Color pigments which reflect UV radiation expand the spectrum of colors which can be differentiated. For example, several blossoms which may appear to humans to be of the same yellow color will appear to bees as having different colors (multicolored patterns) because of their different proportions of ultraviolet.

Powers of orientation: Frisch’s investigation of a bee’s powers of orientation were significant. He discovered that bees can recognize the desired compass direction in three different ways: by the sun, by the polarization pattern of the blue sky, and by the earth’s magnetic field, whereby the sun is used as the main compass, with the alternatives reserved for the conditions arising under cloudy skies or within a dark beehive.

Polarization pattern: Light scattered in a blue sky forms a characteristic pattern of partially polarized light which is dependent on the position of the sun and invisible to human eyes. With a UV receptor in each of the lens units of a compound eye, and a UV filter oriented differently in each of these units, a bee is able to detect this polarization pattern. A small piece of blue sky is enough for a bee to recognize the pattern changes occurring over the course of a day. This provides not only directional but also temporal information.

Variations in the daytime position of the sun:  von Frisch proved that variations in the position of the sun over the course of a day provided bees with an orientation tool. They use this capability to obtain information about the progression of the day deep inside a dark beehive comparable to what is known from the position of the sun. This makes it possible for the bees to convey always up-to-date directional information during their waggle dance, without having to make a comparison with the sun during long dance phases. This provides them not only with alternative directional information, but also with additional temporal information.

Internal clock: Bees have an internal clock with three different synchronization or timekeeping mechanisms. If a bee knows the direction to a feeding place found during a morning excursion, it can also find the same location, as well as the precise time at which this source provides food, in the afternoon, based on the position of the sun.

Horizontal orientation of the honeycomb: Based on the magnetic field, the alignment of the plane of a honeycomb under construction (e.g., the new honeycomb of a swarm) will be the same as that of the home hive of the swarm, according to Karl von Frisch. By experiment, even deformed combs bent into a circle can be produced.

Sensing the vertical: The vertical alignment of the honeycomb is attributed by Karl von Frisch to the ability of bees to identify what is vertical with the help of their head used as a pendulum together with a ring of sensory cells in the neck.

Knowledge about feeding places can be relayed from bee to bee. The means of communication is a special dance of which there are two forms:

Round dance

The “round dance” provides the information that there is a feeding place in the vicinity of the beehive at a distance between 50 and 100 meters, without the particular direction being given. By means of close contact among the bees it also supplies information about the type of food (blossom scent).

The foraging bee… begins to perform a kind of “round dance”. On the part of the comb where she is sitting she starts whirling around in a narrow circle, constantly changing her direction, turning now right, now left, dancing clockwise and anti-clockwise, in quick succession, describing between one and two circles in each direction. This dance is performed among the thickest bustle of the hive. What makes it so particularly striking and attractive is the way it infects the surrounding bees; those sitting next to the dancer start tripping after her, always trying to keep their outstretched feelers on close contact with the tip of her abdomen…. They take part in each of her manoeuvrings so that the dancer herself, in her mad wheeling movements, appears to carry behind her a perpetual comet’s tail of bees.

The waggle dance

The “waggle dance” is used to relay information about more distant food sources. In order to do this, the dancing bee moves forward a certain distance on the vertically hanging honeycomb in the hive, then traces a half circle to return to her starting point, whereupon the dance begins again. On the straight stretch, the bee “waggles” with her posterior. The direction of the straight stretch contains the information about the direction of the food source, the angle between the straight stretch and the vertical being precisely the angle which the direction of flight has to the position of the sun. The distance to the food source is relayed by the speed of the dance, in other words, by the number of times the straight stretch is traversed per unit of time. The other bees take in the information by keeping in close contact with the dancing bee and reconstructing its movements. They also receive information via their sense of smell about what is to be found at the food source (type of food, pollen, propolis, water) as well as its specific characteristics. The orientation functions so well that the bees can find a food source with the help of the waggle dance even if there are hindrances they must detour around like an intervening mountain.

Here is a superb 7 minute documentary that lays out all this information clearly.  It staggers the mind.

As to a sense of hearing, Karl von Frisch could not identify this perceptive faculty, but he assumed that vibrations could be sensed and used for communication during the waggle dance. Confirmation was later provided by Dr. Jürgen Tautz, a bee researcher at Würzburg University’s Biocenter.

The linguistic findings described above were based on Karl von Frisch’s work primarily with the Carnica variety of bees. Investigations with other varieties led to the discovery that language elements were variety-specific, so that how distance and direction information is relayed varies greatly.

Frisch’s honey bee work included the study of the pheromones that are emitted by the queen bee and her daughters, which maintain the hive’s very complex social order. Outside the hive, the pheromones cause the male bees, or drones, to become attracted to a queen and mate with it. Inside the hive, the drones are not affected by the odor.

I was going to find a nice honey recipe, but I am sure you already have plenty. Instead I decided on honeycomb, a childhood favorite, and still very much in my top 5 sweet treats. As a boy in Australia, getting a bag of honeycomb was the highlight for me of the annual family trip to the state fair. It is not actually made with honey, although I imagine you could use it. For those unaware of this ambrosia, honeycomb is a sugary toffee with a light, rigid, sponge-like texture. Its main ingredients are typically brown sugar, golden syrup (or molasses or corn syrup) and baking soda, sometimes with an acid such as vinegar. The baking soda and acid react to form carbon dioxide which is trapped in the highly viscous mixture. When acid is not used, thermal decomposition of the baking soda releases carbon dioxide. The lattice structure is formed while the sugar is liquid, then the toffee sets hard. You have to eat it quickly after making it (not a problem for me), or store it in an airtight container because it quickly absorbs moisture from the air.

In some regions it is often made at home, and is a popular recipe for children. It is also made commercially and sold in small blocks, or covered in chocolate, popular examples being the Crunchie and Violet Crumble bar.

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Honeycomb toffee is known by a wide variety of names including:

honeycomb in South Africa, Australia, and Britain
cinder toffee in northern England
puff candy in Scotland
hokey pokey in Cornwall and New Zealand (especially in the Kiwi classic Hokey Pokey ice cream).
sponge candy (“tire éponge”) in Canada, Milwaukee, Wisconsin, St. Paul, Minnesota, Western New York, and Northwest Pennsylvania, USA
sea foam in Maine, Washington, Oregon, Utah, California and Michigan, USA
fairy food candy or angel food candy in Wisconsin, USA
puffed molasses in Kentucky, USA

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I’m happy with a big bag of lumps of honeycomb or a Crunchie bar.  But you can use it in a host of ways. Crumbled and stirred into vanilla ice cream it moves the soul. Sprinkle it on anything you want to make magical.  I prefer to use golden syrup to make honeycomb, but you can use molasses or dark corn syrup. In the US you can get Tate and Lyle’s golden syrup easily online and in some supermarkets.

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Honeycomb

Ingredients

200 g/7 ozs caster sugar

4 tablespoons golden syrup

1 tbsp bicarbonate of soda

Instructions:

Put the sugar and syrup into a deep saucepan (it bubbles and froths a lot), and stir together to mix. DO NOT stir once the pan is on the heat. At this stage the mix will be solid and lumpy.

Place the pan on medium-high heat. The mixture will first melt, then turn to a viscous liquid, and then to a bubbling mass. Cook for 3 or 4 minutes until it is the color of maple syrup.

Take the mix off the heat, whisk in the bicarbonate of soda and watch the syrup turn into a whooshing cloud of aerated pale gold.

Turn this immediately on to a greased 8” square baking tin lined with baking parchment or greased foil.

Leave until set, about 3 hours, and turn out. Bash into lumps or break apart. Store in an airtight container.