These two bodies have been produced by the longitudinal division or fission of a single body.
In the case of Paramoecium the process of multiplication is slightly more complex than that of Amoeba in the fact that sometimes before the simple fission of the body takes place the interesting phenomenon of conjugation occurs.
The production of new individuals is accomplished in Amoeba by a simple division or fission of its body (a single cell) into two practically equivalent parts.
The hereditary units then grow, divide into two and are uniformly distributed by the fission of the chromosomes between their longitudinal halves.
In animal cells these fibrillae in the cytoplasm centre on definite bodies (Their existence and their multiplication by fission were demonstrated by E.
For a fuller explanation of the fission process, see Our Atomic World, another booklet in this series.
That idea turned out to be correct, and fission tracks have now been found in almost every common mineral (since almost all minerals contain small amounts of uranium).
When the atom suddenly fissions, it breaks in two with considerable energy, and the two fissionfragments rip like cannon balls through the surrounding crystalline structure in opposite directions, creating havoc along the way.
Illustration: Tracks of uranium fission from a fossil antelope bone fragment from Hopefield, Cape Province, South Africa.
The etching brings out the fission tracks so they can be seen (usually as little conical pits) and counted under a microscope.
The fission clock method works this way: A cleavage face or a polished surface of a crystal or glass fragment is etched with a suitable solvent.
That means that only about one spontaneous fission occurs in uranium-238 for every 2 million alpha decays.
They reasoned that a region so intensely disturbed by the passage of a fission fragment should be etched more easily and deeply than the undisturbed surrounding crystal.
The process was known for a long time before anyone was able to find these fission tracks (the damaged tubes) in the crystals.
One striking fact about uranium fission was the large amount of energy it released.
To test this, a quantity of uranium was gathered in the hope that a controlled chain reaction of uranium fission could be established.
The uranium fission process was studied at once to see if neutrons were actually given off and a number of different physicists, including Szilard, found that they were.
The Discovery of Fission But let us get back to the bombardment of uranium with neutrons research that Fermi had begun.
Unfortunately, only a small proportion of the fission products can be put to profitable use.
It is not the budding out or spontaneous fission of certain segments, but the transformation in a definite and very peculiar manner of parts which already exist into other and more complex parts.
Multiplication by spontaneous fission seems from some recent researches to be much less frequent than has been supposed, and more evidence is required as to the fact of the habitual propagation of any planariæ in this fashion.
The existence of the gemmules is a first unknown element; the propagative affinity of the gemmules is a second; their germinative affinity is a third; their multiplication by fission is a fourth--and what an unknown element!
One of the parts formed by fission in certain Protozoa.
Many of the species are phosphorescent; others are remarkable for undergoing strobilation or fission and for their polymorphism.
Defn: One of the two elongated vibratile young formed by fission of the embryo during the development of certain Gregarinæ.
Note: Many of the species are phosphorescent; others are remarkable for undergoing strobilation or fission and for their polymorphism.
Defn: A process of reproduction intermediate betweenfission and gemmation.
Defn: A combining form denoting division or cleavage; as, schizogenesis, reproduction by fission or cell division.
Defn: An order of Schizophyta, including the so-called fission fungi, or bacteria.
Defn: That form of reproduction which requires but one parent, as in reproduction by fission or in the formation of buds, etc.
The bacteria, as has been stated, reproduce by division but the others characteristically by budding or gemmation, though the fission yeasts also by division.
Possibly the spore represents a very rudimentary beginning of a reproductive function such as is gradually evolved in the higher thread bacteria, the fission yeasts, the yeasts, the molds, etc.
In the ordinary microscopical examination of portions of an infusion containing these organisms, an observer may watch for hours and never see a single instance of such fission occurring.
That they are independent organisms derived by fission or gemmation from pre-existing Bacteria and Torulæ.
However well this process of fission may have been established, as a frequent mode of reproduction of Bacteria, such a fact does not lend any support to the notion that these are necessarily distinct and independent organisms.
The process of fission must, however, be considered as the result of a new effort at equilibrium, which has, perhaps, been necessitated by molecular changes that have occurred during a preceding period of growth.
Owing to the absence of a definite membrane, a distinction between fission and internal cell division can scarcely be made here.
The process is somewhat different from ordinary fission and is called budding (Fig.
Fission is the commonest form of cell multiplication throughout the vegetable kingdom.
The nuclear fragments of heavy-element fission which are of greatest concern are those radioactive atoms (also called radionuclides) which decay by emitting energetic electrons or gamma particles.
The energy released in this fission process is many millions of times greater, pound for pound, than the most energetic chemical reactions.
Fission requires that a minimum amount of material or "critical mass" be brought together in contact for the nuclear explosion to take place.
The smaller nuclear weapon, in the low-kiloton range, may rely solely on the energy released by the fission process, as did the first bombs which devastated Hiroshima and Nagasaki in 1945.
The more efficient fission weapons tend to fall in the yield range of tens of kilotons.
However, thefission process is still necessary to achieve the high temperatures and pressures needed to trigger the hydrogen fusion reactions.
Fortunately, one youngster asked his father entirely too many questions concerning the actual fabrication offission weapons.
Perhaps the most startling case of all," Ambly went on, "concerns the Nuclear Fission Society of Urania, Nevada.
Binary and Multiple Fissionin Hexamitus, by Olive Swezy.
On Binary and Multiple Fissionin Giardia muris (Grassi), by Charles Atwood Kofoid and Elizabeth Bohn Christiansen.
The peculiar serpentine form of the corallite is produced by the animal growing in one direction, fission being incomplete, and new mouths being successively opened until a line of them extends along a common stomach.
The way in which the budding or the fission takes place determines the shape of the colony, or corallum, which has a great variety of forms.
The difference between the division of the crystal and the fission of the cell is small in kind; much less than that later differentiation in genesis into parthenogenesis and sexual reproduction.
A fission visible as far away as our system must be a terrible thing.
It's unfortunate that no ships from our system came this far, but then we had no reason to suspect intelligent life until we saw the fission glow in the sky.
It was an atomic fission we saw, all right," he said presently.
Most of the highly radioactive fission products would be blown into space, but some would be drawn back by the asteroid's slight gravity.
He sliced off the inner side where it tapered to a cone, then, working only by eye estimate, cut out a hole in which the wedge of fission material would fit.
Part of his physics training had been concerned with fission and its various applications.
If you do, we'll havefission right here in the open.
If the pieces weren't brought together rapidly enough, the mass would fission in a slow chain reaction with no explosion.
It had to be complicated to keep the pieces of the fissionable material apart until a chemical explosion drove them together fast and hard enough to create a fission explosion.
In Protula Dysteri, as shewn by Huxley, there is a simple fission into two in the way described.
Thus in the springing Monad, described by Drysdale and Dallinger, a form produced by the fission of a monad in an amoeboid condition fuses with an ordinary monad to produce an individual, which then breaks up into spores.
The true asexual modes of reproduction amongst the Metazoa consist of fission and gemmation.
Both fission and gemmation when incomplete lead to the formation of colonies.
Reproduction by fission consists simply in the division of the organism into two similar parts, the nucleus when present becoming divided simultaneously with the cell body.
In Syllis (Quatrefages) fission takes place, the parent form dividing into two, of which only the posterior after its detachment develops sexual organs.
The gamma rays on the other hand are emitted by the atomic nuclei themselves when they are transformed in the fission process.
This generates from the fission products and continues for about one minute until all of the explosion products have risen to such a height that the intensity received on the ground is negligible.
The nuclear fission of a pound of uranium would produce an equal temperature rise in over 200 million pounds of water.
No casualties were suffered as a result of any persistent radioactivity of fission products of the bomb, or any induced radioactivity of objects near the explosion.
Budding is a form of fission in which a small projection is formed on the parent cell and then cut off, making a new individual.
Budding#, a form of fission in which a cell or portion of the body forms a small protuberance or bud, which is then cut off from the parent and forms a new individual.
Simple fission requires but a short period of time to be complete.
Slow neutrons, on the other hand, can enter nearly all atomic nuclei and induce fission of certain of the heavier ones.
The discovery of fission attended by the release of enormous amounts of energy led to feverish activity on the part of physicists and chemists everywhere in the world.
Element 61 was made for the first time from the fission disintegration products of uranium in the Clinton (Oak Ridge) reactor.
Surely you don't intend to carry fission or fusion weapons against them?
Reproduction by fissionoccurs rarely in the Indian Hydra, but both equal and unequal vertical fission have been observed.
In the case of equal fission the circumoral area lengthens in a horizontal direction, and as many extra tentacles as those the polyp already possesses make their appearance.
It appears that, even in favourable circumstances, for a fresh polyp to be formed by artificial fissionit is necessary for the piece to contain cells of both cell-layers.
