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Final Answers
© 2000-2023   Gérard P. Michon, Ph.D.

 Rod of 
Asclepius

Medicine

When I woke up just after dawn on September 28, 1928, I certainly didn't plan to revolutionize all medicine by discovering the World's first antibiotic.
Sir Alexander Fleming (1881-1955; Nobel 1945)
 
In memoriam:  Paul Guillebaud  (1943-2018).

 

Related articles on this site:

Related Links (Outside this Site)

Concentrations of blood glucose (bG) in  mg/dL  (cg/L)  or  mmol/L.
Hemoglobin A1c Test
Wikipedia: Glycemia  |  Glycosylated Hemoglobin
 
border
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 Pierre Jean Georges Cabanis 
 1757-1808  Jean-Nicolas Corvisart 
 1755-1821  William Harvey 
 1578-1657  Andreas Vesalius 
 1514-1564  Paracelsus 
 1493-1541

Medicine by the Numbers

 Guillaume Dupuytren 
 1777-1835  Joseph Lister 
 1827-1912  Emil Adolf von Behring 
 1854-1917
It is with medicine as with mathematics:  We should 
occupy our minds only with what we continue to know;
what we once knew is of little consequence.

Charles Augustin  Sainte-Beuve   (1804-1869) 

(2010-08-02)   What is the normal human body temperature?

The usual answer is a simple rule of thumb:  37°C  or  98.6°F  (same thing).  This traditional estimate of normal body temperature is originally based on the findings of Dr. Carl Wunderlich (1815-1877)  who recorded about a million armpit temperature measurements on  25 000  patients.

When Gabriel Farhenheit devised his temperature scale in 1714, he  meant  100°F to be the normal temperature of the human body.  However, this turns out to be only a rough estimate which is not appropriate for clinical thermometry  (either the measurement wasn't accurate or Fahrenheit was running a slight fever at the time).

Modern studies  (1992)  have found the average normal temperature for adults to be close to  98.2°F  (36.8°C).  Older people usually have lower mean body temperatures, which are normally well below  98.6°F.

The traditional threshold for fever is  38°C  (100.4°F).  However, body temperature does depend on the time of day.  For women, it also varies with the phase of the menstrual cycle, which may translate into a higher baseline body temperature.

It's thus more accurate to base a diagnosis on a curve of the average body temperature recorded at different times of the day when the person was known to be in good health.

Note that the normal  body temperatures  of various warm-blooded animals depends strongly on their species  (it's about  42°C  for a healthy chicken).

Normal Body Temperature: Rethinking the normal human body temperature   (Harvard Health Letter)


(2010-08-02)   What is the normal human arterial blood pressure?

During a normal heartbeat, the blood pressure varies between a minimum  (diastolic)  and a maximum  (systolic).  Both numbers are usually expressed in  mmHg  (millimeters of mercury)  or  torrs  (those two units are used interchangeably;  the minute difference between them makes no clinical difference whatsoever).

In some countries  (France, etc.)  medical instruments are usually graduated in  centimeters  of mercury instead  (cmHg).  A typical blood pressure might thus be given as  130/80  in the US and  13/8  in France.

Blood pressure should be measured at the level of the heart itself.  This is one reason why it's usually measured on the upper arm  (the hydrostatic pressure difference between the heart and the lower leg of a standing person is about  80 mmHg).  Readings can be influenced by many begnign factors, including posture and recent physical activity.

The normal blood pressure of a healthy person will typically be between  90/60  and  120/80.


(2010-08-02)   What is the normal pulse rate in humans at rest?

At rest, a healthy human heart beats at a rate of about 60 pulsations per minute  (1 Hz).  The pulse rate of trained athletes can be much lower and the heartbeat of sedentary people is often faster...

During and after a substantial effort, the pulse of a person quickens.


 Coat-of-arms of 
 William Harvey (2012-08-24)   Circulation of the blood
It was first described in 1628, by William Harvey (1578-1657).

For more than a thousand years, the teachings of  Galen (AD 129-217)  were not questioned by medical students or their teachers.  In particular, it was thought and taught that veinous blood was produced by the liver and consumed by the rest of the body.  The first success story of modern experimental medecine was to prove that it ain't so.

In 1628, Harvey (1578-1657)  estimated  extremely  conservatively that the heart pumps no less than 540 pounds of blood per day  (modern estimates are nearly 30 times larger; around  7 tons  per day).  Clearly, the liver could not possibly  produce  that much blood...  Blood  has to  circulate!

 Mammalian Blood Circulation   The heart of mammals is a double pump  (a full circuit of the blood goes through the heart twice).  The right half of the heart pulls the blood from the veinous network through the two large  venae cavae  and pushes it into the  pulmonary artery.  The left part of the heart pulls blood back from the  pulmonary vein  and pushes it into the arterial network  (aorta, carotid, etc.)
 
In either half of the heart, blood enters into the  atrium  (part of which is the  auricle )  and it's expelled from the  ventricle.

BBC Video :   William Harvey's discovery of the circulatory system  by  Michael Mosley


(2012-08-25)   Respiration  is a slow form of combustion   (1780)
The joint work of  Lavoisier  (1743-1794) and  Laplace  (1749-1827).

It is the role of the lungs to continuously convert veinous blood into arterial blood (with oxygen-rich hemoglobin).  All other human tissues take oxygen from blood and reject carbon dioxide in it.  As the reverse process takes place in the lungs,  respiration  appears chemically to be a form of slow  combustion,  as was first established by Laplace and Lavoisier in 1780.


(2010-08-02)   What dietary caloric intake is considered normal ?

The caloric intake should compensate for the expenditure of energy spent on basic metabolic functions and physical efforts.  If the intake is more than that, then it is stored the form of body fat.  That fat is burned as needed when more energy is required than what is provided by the daily intake.

A very rough rule of thumb is that a person burns about 100 W of power  (power is the energy spent per unit of time).  One watt  (W)  is a joule  (J)  per second.  A  calorie  (cal)  per second is  4.184 W.

The unit of energy used by dieticians is the so-called dietary calorie, large calorie or kilocalorie  whose proper symbol is  kcal  (the confusing capitalized symbol  "Cal"  was once popular but it's now deprecated).

1 kcal   =   1000 cal   =   4184 J

If you burn  100 W  continuously for a full day  (24 h  is  86400 s)  you will have burned  8 640 000 J  or about  2065 kcal.

Typically a reasonably active average man will consume energy at the above rate  (2000 kcal/day)  and should compensate for it by an equal food intake.  The need of other individuals may vary.  For example, a young woman may only need  1200 kcal/day  or less.


Dr. Rita Rae Fontenot (2006-10-19)   Emergency use of an IU rating.
How do I give 125 IU from poorly-labeled 10 mL vials of 10000 units?

This amounts to 1000 IU per mL.  8 doses per mL.  To administer such a small dose (2 drops) with some precision, you may want to dilute it first.  For example 1 vial in 90 cc of an inactive solution yields 100 cc, from which you get 80 doses of 125 IU (1.25 cc each).  If you're a young doctor by herself in a remote area, I'll just pray that you'll know what to do with whatever means you have at your disposal and whatever help you can gather about this emergency.

What is an  IU  worth ?

The IU (International Unit) is a unit of biological activity which is standardized for each substance (fairly arbitrarily) by the World Health Organization.  It's also abreviated UI (from the French locution  unité internationale ).

For a simple chemical (e.g., Vitamin C) the WHO simply assigns a value of 1 IU to a particular mass of that substance.  The rating of biological preparations (e.g., vaccines) is more delicate but it need not be of concern to the practitioner...

If you need to give 125 IU of a substance to a patient, you must first know the concentration of the solution you have at hand.  Normally, this is shown directly in IU/ml, IU/mL or IU/cc (same thing) on the package.  It could also be given as the reciprocal of that:  For example 1mL/40 IU is the same as 40 IU/mL.


(2007-03-29)   Concentration is amount (grams or moles) per volume.
Blood glucose concentration (bG) is thus given in mg/dL or in mmol/L.

A mole of glucose  (CAS 50-99-7)  weighs  180.16 grams.  Therefore, a blood glucose concentration  (bG)  of  1 mmol/L  is equivalent to  18.016 mg/dL.

The blood glucose concentration given in  mg/dL  (the form most commonly used by doctors and diabetic patients across Europe and the US)  is thus about 18 times the number in  mmol/L  (often used in medical research).

Blood Glucose, Plasma Levels   (bG)
mg/dLmmol/L   Interpretation and/or Symptoms  
54030.0 Severe imbalance.
36020.0 Very high blood sugar level.
27015.0 High or very high blood sugar
(depending on patient)
20011.1
18010.0 Non-diabetic postprandial
(i.e., after meal)
1448.0
1086.0 Non-diabetic preprandial
(i.e., before meal)
100 5.55 
905.0
724.0 Slightly low.  Mild lethargy.
543.0 Low blood sugar level.  Lethargy.
362.0 Extremely low.  Risk of fainting.

Whole blood concentration is actually 15% lower than the plasma level quoted above, but modern portable glucose meters are calibrated to match the plasma readings obtained in lab tests.  Venous blood and capillary blood may have slighlty different compositions only when blood chemistry evolves rapidly (after a meal).


(2007-03-29)   Blood Glucose and HbA1c
Glycated hemoglobin buildup indicates average blood glucose (bG).

The table below gives the rough correspondence between HbA1c results (in %) and  long-term average  blood glucose level (bG in mg/dL).  It is based on the following approximative formula:

(mean bG, in mg/dL)     =     35.6  (% of A1c hemoglobin)  -  77.3

HbA1c 4.04.14.24.34.44.54.64.74.84.9
Glucose 65697276798386909497
 
HbA1c 5.05.15.25.35.45.55.65.75.85.9
Glucose 101104108111115119122126129133
 
HbA1c 6.06.16.26.36.46.56.66.76.86.9
Glucose 136140143147151154158161165168
 
HbA1c 7.07.17.27.37.47.57.67.77.87.9
Glucose 172175179183186190193197200204
 
HbA1c 8.08.18.28.38.48.58.68.78.88.9
Glucose 208211215218222225229232236240
 
HbA1c 9.09.19.29.39.49.59.69.79.89.9
Glucose 243247250254257261264268272275
 
HbA1c 10.010.110.210.310.410.510.610.710.810.9
Glucose 279282286289293297300304307311
 
HbA1c 11.011.111.211.311.411.511.611.711.811.9
Glucose 314318321325329332336339343346
 
HbA1c 12.012.112.212.312.412.512.612.712.812.9
Glucose 350353357361364368371375378382
 
HbA1c 13.013.113.213.313.413.513.613.713.813.9
Glucose 386389393396400403407410414418
 
HbA1c 14.014.114.214.314.414.514.614.714.814.9
Glucose 421425428432435439442446450453

Blood Sugar and Diabetes (19:34)  by  Dr. Eric Berg,  Chiropractor  (2013-04-02).


(2018-09-10)   Human Fat   C55H104O6

The mathematics of weight loss (21:25)  by  Ruben Meerman  (TEDx [edited]  2013-10-10).
 
How the Krebs cycle powers life and death (55:58)  by  Nick Lane  (TEDx [RI  2022-08-04).


(2021-07-10)   Body Mass Index   (BMI in kg/m2 )
BMI   =   (Weight in kilograms) / (Height in meters)2
BMI   =   703.07 × (Weight in pounds) / (Height in inches)2

As a rule of thumb for adults,  a normal BMI is between 18.5 and 25.  Obesity (class I) starts at 30.  Extreme obesity (class II) starts at 35 and severe obesity (class III) at 40.

Conversely,  the healthy weight of a person of height h is between  18.5 h2  and  25 h2.

The idea was developed between 1830 and 1850 by the Belgian statistician  Adolphe Quételet (1796-1874)

Standard classification by weight, according to BMI  (in kg/m2 )
17 kg/m218.5 kg/m2 25 kg/m230 kg/m2 35 kg/m2
Underweight Normal Overweight Obese

The BMI doesn't scale correctly, since people of the same shape have a weight proportional to the cube of their height.  The BMI is thus a very poor basis for classifying very short or very tall people.  The so-called  ponderal index  (in kg/m)  has been advocated instead.

Wikipedia   |   CDC


(2012-02-18)   Medical Abbreviations
Traditionally used on prescriptions and elsewhere.

Quid quid latine dictum sit, altum videtur.
Anything stated in Latin is perceived as profound.

Abbr.Read as (Latin)English translationUsage notes
q7d once a week 
QOD
q2d
 every other day 
QDquaque dieonce a day 
SID (veterinary medicine)
BIDbis in dietwice a dayMorning and evening.
TIDter in diethree times a dayMorning, noon, evening.
QIDquater in diefour times a dayMorning, noon, evening, nighttime
q4hquaque 4 hevery 4 hours6 times a day (including sleeptime)
q2h
QOH
quaque 2 hevery 2 hours
every other hour
12 times a day
PRNpro re nataas neededwhenever symptoms call for it

Scholarly abbreviations


(2016-03-20)   Mosquito-borne diseases.
They're eradicated below a certain ratio of local mosquitoes per human.

Such diseases are transmitted by specific species of mosquitoes.

  • Dengue  (in French: la dengue, le petit palu, la fièvre rouge).  At least five different types of viral infections.  Each infection normally lasts only 2 to 7 days and subsequently provides lifelong immunity to one serotype only  (with short-term immunity to other types).  The risk of life-threatening complications is increased by multiple infections.
  • Yellow fever  (in French: fièvre jaune, vomi noir).  First human virus ever isolated  (1927).  Spread by female  Aedes aegypti.
  • Chikungunya.  In 2005 and 2006,  an epidemic of  chikungunya  infected nearly one third of the population in  French Reunion Island.
  • West Nile virus (WNV). 
  • Zika virus  (2015 outbreak).
  • Malaria.  (French: paludisme)  The key example discussed below.

Malaria  was known in Europe since antiquity.  The parasite responsible for the disease was first identified in the blood of infected patient by the French military physician  Alphonse Laveran in 1880.  Malaria is still causing hundreds of thousands of deaths every year, mostly in Africa.

In 1897 the fact that malaria was actually transmitted by mosquito bites was discovered in India by the British military physician  Ronald Ross (1857-1932; Nobel 1902).

In 1911,  it was Ross himself who first stated a surprising mathematical fact, which he called  the mosquito theorem :  Malaria is locally eradicated as soon as the number of mosquito per inhabitant falls below a certain predictable threshold.  (Thus, it's not necessary to get rid of every single mosquito.)

Considering a constant local population of  N  humans and  n  mosquitoes,  Ross  assumed that every mosquito  (infected or not)  would inflict an average number of  f dt  bites over a small interval of time  dt.  Both the biting mosquito and the biten human become infected if either one of them was infected before the bite.

The number of infected humans and mosquitoes are respectively approximated by two continuous functions of time,  I(t)  and  i(t).

The Ross Model :

In the time-scale of interest, Ross neglected the natural demographic occurences of human births and deaths.  The healing rate among humans is a constant  g.  The number  I(t)  of infected humans thus obeys the following  differential relation  (the first term accounts for infected mosquitoes biting a healthy human and the second term pertains to newly-healed humans):

dI(t)/dt   =   i(t) [ 1 - I(t)/N ] f  -  I(t) g

On the other hand, infected mosquitoes never heal.  However, they're always born uninfected and their mortality rate  m  ends up playing the same mathematical rôle as the healing of humans  (under the assumption that the mosquito population is constant, their mortality-rate equals the birth-rate).

di(t)/dt   =   I(t) [ 1 - i(t)/n ] f  -  i(t) m

Stationary Rates of Infection  (Ronald Ross, 1911) :

Ross remarked that the infected populations were stationary when both of the above variations vanished, namely when:

  • i [ 1 - I/N ] f   =   I g
  • I [ 1 - i/n ] f   =   i m

Dividing those two equations into  i I,  we obtain two linear relations between  1/I  and  1/i:

i  ( N + m )   =   I  ( n + g )

Thus, the first equation multiplied into  ( N + m )  becomes:

I  ( n + g )  [ N - I ] f   =   I g  ( N + m )

This equation in  I  has a trivial solution  (I = 0)  and a nontrivial one:

I   =   ( nN - gm )  /  ( nf + gf )

Dynamics of Malaria  (Alfred Lotka, 1923) :

 Come back later, we're
 still working on this one...

Mosquito-borne diseases   |   Elephantiasis
"Le modèle de Ross" by N. Bacër  (Tangente Hors Série, 58, pp 34-35. Feb. 2016)


(2016-03-11)   Propagation of epidemics.
Predictions based on the simplest mathematical model  (SIR).

The first simplified theoretical model which explained general epidemics was proposed in 1927 by  William Kermack  (1898-1970)  and  Anderson McKendrick  (1876-1943).  That model considers just three  compartments  of the total population  (dead or alive)  whose importance vary with time (t).  It's assumed that an individual becomes fully contagious upon infection,  a condition which ends abruptly with total recovery or death  (because corpses are normally isolated).

  • S(t) :   The number of individuals  susceptible  of getting the disease.
  • I(t)  :   The number of  infectious  people  (infected and contagious).
  • R(t) :   The remainder  (people who have either  recovered  or died).

As the dynamics of a typical epidemic is much faster than the normal demographics of birth and death,  it can be assumed that the sum of the three compartments is constant. 

In a new viral disease;  S(t)  decreases at a rate  dS/dt  proportional to the number of contacts between the unexposed population  S  and the contagious population  I.  The number R(t) of recovered or dead individuals simply decays at a constant rate  c  (combining proper recovery and mortality rate).

In other words,  the following  differential equations  are satisfied:

dS
Vinculum
dt
   =    - b S I  
dI
Vinculum
dt
   =    b S I - c I
dR
Vinculum
dt
   =      c I

In the language of  differential forms the first two equations become:

dS   =   -b S I dt       and       dI   =   (b S - c) I dt

Changing the variable from  t  to  u  with  du  =  I dt,  we have:

dS   =   -b S du       and       dI   =   (b S - c) du   =   -dS - c du

This yields   S  =  S(0) exp(-b u)   which we plug into the second relation:

dI   =   [ b S(0) exp(-b u) - c ]  du

Before we integrate that,  we must point out that only positive values of the quantity  I  are acceptable  (which does make u an increasing function of t).  So the epidemic dies out immediately  (when I(0) is tiny)  if  dI  is negative at  (u=t=0)  which happens when   b S(0) ≤ c.  Otherwise:

I(u)   =   I(0)  +  S(0) [ 1 - exp(-b u) ]  -  c u
 
S(u)   =   S(0) exp(-b u)

The maximum of  I  (dI = 0)  occurs when  b S(0) exp(-b u) = c.  Namely:

Imax   =   I(0) + S(0) - c/b  -  c umax
umax   =   Log ( b S(0) / c ) / b

Introducing the parameter  R0   =   b S(0) / c,  this boils down to:

Imax   =   I(0) + S(0)   R0 - 1 - Log R0
Vinculum
R0

As the number of infected people who require professional medical attention can be assumed to be a fixed proportion  k  of the number  I(u)  of infected people,  k Imax  is the minimum capacity the healthcare system should have in order not to be overwhelmed  (in which case people who could have survived will die).  If that capacity is inadequate,  the only acceptable solution is to take forceful confinment measures to lower  R0  to reduce  Imax  (which epidemiologist call  flattening the curve).  This also delays the peak and may buy some precious time to increase capacity  (summoning reserve personnel, training volunteers, installing new beds, manufacturing ventilators, etc.)

I have to confess that I am slightly annoyed by the many younger YouTube mathematicians who have spoken out in the wake of the COVID-19 pandemic.  They assert,  without having even tried,  that the above is "difficult to solve" because the equations are nonlinear.  This ain't so; not all nonlinear equations are difficult.  The basic model and its solution do provide a useful baseline which is easy to understand without computer simulations and obscure comments thereof.  What's difficult is to devise more realistic models  (for which numerical methods are fully justified)  and devise effective countermeasures in a complex world.  Simplified assumptions are just a first step.

Like any mathematical model,  this is an oversimplification of reality.  So is Galileo's  law of falling bodies  obtained by  neglecting  air resistance.  In both cases,  it's still a good thing to master the basic mathematics involved in order to understand how and why reality deviates from the idealized models.

Intro to the SIR Model (15:34)  by  Trefor Bazett  (2020-03-11).
 
Compartmental models in epidemiology
Exact solutions of the SIR epidemic model  by  Harko, Lobo & Mak  (2014-03-10).
La propagation des épidémies  by  Hervé Lehning  (Tangente Hors Série, 58, pp 28-30. February 2016).


(2020-03-27)   Recovering from a Pandemic
To save lives,  everyone should try to get infected as late as possible.

This is being written in the middle of the  COVID 19  pandemic,  shortly after the twentieth Birthday of this site  (created  on 2000-03-19,  precisely to promote a proper  mathematical  understanding of the world around us).  Such a basic understanding is invaluable not only to policymakers and their advisers but also to the general public,  who might otherwise reject unpopular measures like confinment:  The main issue here is not self-preservation but  solidarity.  Let's be blunt:

Every infection  delayed  saves the lives of  others.

This is so because those who get  very  sick cannot survive without the medical attention provided by limited number of health workers and a limited number of hospital beds.  If a virulent disease is allowed to run its course unchecked,  everyone gets sick at the same time and the health system is overwhelmed.  This results in needless deaths.

Preventive confinment will not necessarily reduce the total number of infected people but it may slow down the spread of the disease just enough to prevent needless deaths by limiting the maximum number of serely ill people at any given time so that the health care system can handle them.

The second wave :

Governments are prompted into confinement policies once the death toll rises.  Public support is not difficult to garner at first.  However,  the social and economic costs of such measures are such that deconfinment can be expected to be decreed typically too early.  A virus which was potent enough to cause a pandemic from a single case is potent enough to restart it as soon as confiment measures are no longer strict enough.  So,  the epidemic can be expected to rise again,  until one of the following conditions is met:

  • A very large percentage of the population has been contaminated.
  • A vaccine has been made available and administered massively.
  • A miracle cure is promptly found  (highly unlikely).

Ruling out this last possibility,  a vaccine has never been developped in less than one or two years.  Any lesser timeframe is  (overly)  optimistic.

Mathematics of the Corona outbreak (35:59)  by  Tom Britton  (2020-03-13).
 
Un chercheur décrypte l'épidémie COVID-19 (French, 19:26)  by  François Renaud  (2020-03-16).
 
How to Predict the Spread of Epidemics (22:17)  by  Jade Tan-Holmes  (Up and Atom, 2020-03-20).
 
COVID-19: It's just the beginningc (24:12)  by  Joe Scott (2020-03-23).
 
The Coronavirus Curve (22:17)  by  Ben Sparks  (Numberphile", 2020-03-25).
 
Simulating an epidemic (23:11)  by  Grant Sanderson (3Blue1Brown, 2020-03-27).
 
How to tell if we're beating COVID-19 (7:15)  by  Henry Reich   (Minute Physics,  2020-03-27).


(2022-09-09)   Early forms of vaccination by nasal insufflation.


(2019-02-08)   Caffeine  =  Theine  =  Guaranine  =  Mateine
The most widely consumed  psychotropic  substance.

Unlike most other psychoactive substances,  caffeine  is legal and unregulated nearly everywhere.  However,  it's not recommended for children under  12  and it's strongly discouraged for women who are either pregnant or breastfeeding.

A typical cup of coffee contains about  100 mg  of caffeine. 

Caffeine was first identified in 1819 by  Friedlieb Runge (1794-1857)  who was honored by the following  Google Doodle  on his 225-th Birthday:

 Doodle honoring Friedlieb Runge

Caffeine


(2022-08-29)   Eugenol  (clove oil).  Nature's miracle dentistry drug.
Suggested by Thomas Vong, dentist in Paris, France  (7, rue de Langeac).

Cloves  (French  clous de girofle)  is the main source of a traditional remedy now identified as  eugenol,  ubiquitous in modern dentistry.  This chemical is also present in other spices, including:  allspice  (Jamaica pepper, French quatre-épices),  nutmeg  (French noix de muscade),  cinnamon (French cannelle),  basil  (French basilic)  and  bay leaf  (French feuille de laurier).

 Eugenol

Eugenol

C10H12O2     164.2 g/mol
(C6H3 OH OCH3) CH2 CHCH2
4-allyl-2-methoxyphenol
CAS 97-53-0
 97-53-0

This allylbenzene was first obtained in 1834 by  Carl Jacob Ettling (1806-1856)  a former assistant of  Justus von Liebig. The name  eugenol  was coined in 1858 by  Auguste Cahours (1813-1891; X1833)  after  Eugenia caryophyllata,  the former  (Linnean)  name for  cloves  (now best called  Syzygium aromaticum).

Eugenol   |   Zinc Oxide Eugenol (dentistry)   |   Chemical Book
 
Medico-Dental History of Cloves  Nature, volume 151, page 194 (1943-02-13).


(2022-10-25)   DNA,  Genetic Code  and  Forensics.

How They Caught The Golden State Killer (27:11)  by    (Veritasium, 2021-09-30).


(2023-05-17)   Viruses   (Ivanovsky, 1892)
Pathogens smaller than bacteria.

In 1892,   Dmitri Ivanovsky (1864-1920),  passed the sap of tobacco plants infected with s mosaic deasese through a  Chamberland filter,  designed in 1888 by a collaborator of  Louis PasteurCharles Chamberland (1851-1908).  Such a filter will not yet any bacteria through but Ivanovky found that the filtered sap remained infectious,  even at low concentrations.

Mosaic viruses (foliage plants)   |   Bacteriophages (phages)
 
Are viruses older than Life? (26:22)  by  Leila Battison  (History of the Earth, 2021-02-14).


(2023-05-17)   Prions are just misfolded proteins   Infectious agents which transmit a misfolded shape;  without using any genetic material.

Prions   |   Proteinopathy   |   Creutzfeldt-Jakob disease (CJD)   |   Alzheimer's disease   |   Parkinson's disease

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