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Physicists have developed a general theory of defecation

Taras Molotilin, N+1

A team of American scientists has created a hydrodynamic model describing the process of defecation in 43 different representatives of mammals. The researchers also tested the theory experimentally and found out that even very different-sized animals (a domestic cat and an elephant, for example) spend about the same time emptying their intestines. The new work is published in the journal Soft Matter (Yang et al., Hydrodynamics of defecation).

The authors of the study started from the idea that in medicine considerable attention is paid to the analysis of the stool, but at the same time the process of defecation itself, its duration, for example, is deprived of due attention, although it often contains important information about the patient's condition. In addition, from the point of view of physics, no theoretical model has yet been created that can explain the unusual fact that mammals, whose masses may differ by four orders of magnitude, still defecate in the same characteristic time (12 ± 7 seconds). Earlier, another group of scientists had already conducted a similar study on urination (Duration of Urination Does Not Change With Body Size). This paper won the 2015 Nobel Prize in Physics.

Two of its four authors also participated in a new study, the retelling of which, Surprising end-results from prize-winning urination-duration researchers, has already been published on the Improbable Research – VM website.

In the new work, physicists analyzed video materials provided specifically for this study by employees of the Atlanta Zoo, as well as a number of YouTube videos of relevant content. Scientists were interested in the characteristic time of defecation, which, according to the authors, "is determined by the ratio of the length of feces to the speed of feces." In addition, additional data were required to build a mathematical model, in particular, the viscosity of the released material. To do this, the authors carried out rheological measurements. However, this stage was carried out only for samples collected from the enclosures of cats, dogs and rabbits, since larger excrements "... contained too many stones and plant stems and did not fit into the measuring chamber of the device."

The aspect ratio of faeces was also studied separately, on which, among other things, the characteristic time of defecation depended. However, in this aspect, scientists had to exclude some animals (rodents, for example) whose excrement was oval in shape, since "such defecation does not occur in a stationary mode," so only cylindrical feces were discussed in the future.

The hydrodynamic theory itself was based on the fact that for the rapid slipping of feces along the walls of the rectum, the body secretes mucus that has strictly defined rheological characteristics. This liquid belongs to the class of pseudoplastic, that is, its viscosity decreases with increasing shear — the gradient of the flow velocity. Such a system can be described by the Couette model, in which the velocity of the medium is linearly related to the shear value and the thickness of the mucus layer. As a result, the authors obtained an analytical expression linking the characteristic time of defecation with the thickness of the mucus layer, the aspect ratio of cylindrical feces and the amount of rectal pressure.

Analyzing the mathematical expression obtained, the authors note that the ratios of the main parameters of the model practically do not change with increasing animal weight, and, consequently, the characteristic time of defecation should remain constant. Scientists have also created an extension of the model in case an animal suffers from diarrhea or constipation.

According to the researchers, their work will serve as a solid basis for more detailed studies of the physiological processes occurring in the intestines and other organs of mammals. In addition, using a new mathematical model, it is possible to analyze deviations in the characteristic time of defecation and associate them with certain characteristics of the intestine.

The experiments involved warthogs, giant pandas, white rhinos, lions, elephants, zebras, cats, dogs and mice. Not a single animal was injured.

Portal "Eternal youth" http://vechnayamolodost.ru  28.04.2017