Black Death--- A Biological Perspective

Thomas Haren
1991 Woodrow Wilson Biology Institute


During 1346-1350, more than 25 million people died because of "Black Death". The symptoms were visible, painful, large, dark-colored swellings called buboes that were located in the lymph glands.The cause of the disease was uncertain and resulted in many bizarre speculations. In 1894, a Swiss scientist, Alexander Yersin, discovered the bacteria that caused "Black Death". This, however, was not the end of the quest. Three years later, Paul Louis Simond discovered the vector that transmitted the disease from rats to humans.


  1. Describe the symptoms, treatments, and control measures of Black Death.
  2. To introduce students to the scientific method.
  3. To introduce students to a vector disease.


  • paper; pencil; 30 Petri dishes; EMB agar; 6 microscopes; 6 stereoscopic (dissecting) scopes; 6 slides of Xenopsylla cheopis, Pulex irritans, Ctenocephalus canis, and E. coli; fresh culture of E. coli; grease pencil; innoculating loop; bunsen burner; autoclave; 500 ml flasks; distilled water.


(10-15 minutes)

The teacher should use the "splash sheet" of key words as an introduction to the topic. (See "splash sheet" word list at end of this paragraph) It is recommended that you do not give any background information. Divide the class into cooperative learning groups of 3 to 4 students and allow the groups to take the key words and place them into sentence or story form. They can then present these to the class. At the conclusion of the group activity, present correct information that is found below under objective 1. "Splash Sheet"--Place the following "splash" words in large bold print onto an overhead transparency: 25 million; strychnine; 1080; "stinks", 500 years; buboes; bacteria; Yersinia pestis; streptomycin; rats; quick onset; Xenopsylla cheopis; blackened lumps; high temperature; warfarin; fleas; Alexandre Yersin; Rattus rattus.


  1. Symptoms-Characteristics of the disease include-quick onset, high temperature, fast pulse rate, a white coating on the tongue, nervous energy, and mental confusion. Incubation period varies from 2 to 10 days, but is most commonly 4-6 days. Eventually, pain occurs in the groin, axilla (armpit), and neck (all areas that contain lymph glands). Later, intense pain will cause the victim to concentrate on the visible "buboes", the hard lumps that begin to appear on the inner thigh, neck, and axilla. These areas will begin to turn black. Autopsies have reported that the bacteria, Yersinia pestis, has been found in the pericardial sac, spleen, liver, lymph nodes, and bone marrow.

  2. Treatments-Ancient methods of treatment: bathing in human urine; wearing own excrement; placing of "stinks" (dead animals) in your dwelling, use of leeches, and drinking molten gold and powdered emeralds. Modern methods of treatment: best if diagnosed during early onset; the use of sulphonamides was popular in the 1930's; currently, use of streptomycin -the most effective therapeutic agent tested in the treatment of bubonic plague (excellent alternates-chloramphenicol and tetracycline).Penecillin is useless.

  3. Control measures- attempting to control rat populations-use of rodenticides -"1080", "warfarin", barium carbonate, strychnine, arsenic, and phosphorous; fumigation of ships before arriving into port (hydrocyanic gas); use of fox terriers; hunting with firearms; improving sanitary conditions around human habitats; seperate facilities for livestock; attempting to control flea populations -use of insecticides (DDT widely used in 1950's-60's); vaccination of humans only gives a short-lived protection.


(15-20 minutes)

Students work in cooperative teams. Duplicate activity 2 paragraph and distribute to groups. Have students brainstorm, construct, and record an experiment using the scientific method. When completed, have cooperative groups exchange activity sheets and evaluate experimental format. At conclusion of group activity, the teacher should present the information from objective 2.

Activity 2 paragraph: Your cooperating team has been assigned to travel to the Amazon rainforest with a world famous herpetologist, Dr. Pierre Acite. Your expedition has been well-stocked with food, safe drinking water, and unlimited laboratory supplies for field research. Arriving at your destination, you are attacked by hostile cannibals. One of their poison arrows has permanently removed Dr. Acite from the expedition. Your team is taken captive and when you arrive in their village, you notice there are very few children under 4 years of age. More bad news arrives: the tribal chief''s one year old son has contracted an unknown disease. Being an optimisitc group, you seize the opportunity to flaunt your scientific expertise. That night, your team brainstorms observations. You observed that: 1) they drink water directly from the Amazon River; 2) they eat raw pig meat; 3) they do not wash their hands before they eat; and 4) the adults drink cha-cha ( a beverage made from the root of the cha-cha plant). Your goal for this activity is to choose a variable and to contstruct a working experiment. Select your variable and remember a control to compare against the variable. Good luck- use your head or you may lose it!


The scientific method is vital in solving a problem in a logical procession. The steps of the scientific method include:
  1. State the problem
  2. Develop a hypothesis (based on research and observations)
  3. Develop an experiment to test the hypothesis (includes a control and a variable)
  4. Collect and accurately record data
  5. Analyze data for significance
  6. State your conclusion

Humans are visual animals and conduct the majority of their observations through visual stimuli. During the "Black Death" years, noticeable observations were: droughts, famines, climatic changes, the handling of a rat newly dead from plague was dangerous, however, after several hours it could be handled with no danger; rats were not biting people; rats did not exhibit symptoms of plague until near death--staggered as if in a drunken state and easily captured; mass death of rats before the onslaught of plague; observed symptoms in vicitms- buboes--texture, size, and location; fever; and a white coating on the tongue.

The people of 14th century lacked formal educational institutions so they were misled and susceptible to superstitions. Concepts were taken for granted and were not methodically tested. The concept of spontaneous generation, in which living organisms arose from dead matter, was finally disproved by Redi in the 17th century.

The plague bacillus was finally discovered in 1894 in Hong Kong. A Swiss scientist, Alexandre Yersin, who had worked at the Paris Pasteur Institute, discovered the bacteria in tissues of plague victims. He discovered the bacteria, Yersinia pestis, but the vector of the disease eluded him. Shortly after this discovery, Professor M. Ogata, of the Hygiene Institute in Tokyo, proved that fleas contained the plague bacilli that were taken from infected rats. He then suggested that fleas might be the vector of the disease. The final mystery was solved in 1897 by P.L. Simond. The clue that led to his discovery of flea transmission were the bites on the legs of the victims. They appeared as small greyish spots and the presence of these bites always brought about the bubonic swelling in the affected region of the body.


(10-15 minutes)

Part 1: Observing Fleas
The teacher should obtain mounted slides of Xenopsylla cheopis, Pulex irritans, and Ctenocephalus canis. Recommend six slides of each species so a minimum of 6 work stations can be organized. Have students observe the three species of fleas.

  • Xenopsylla cheopi =Indian rat flea
  • Pulex irritans =Human flea
  • Ctenocephalus canis =dog flea

Optional: Teacher can bring in fresh speciemens of fleas obtained from dogs. Place fleas into a container of isopropyl alcohol. This allows students the opportunity to view blood stored inside the abdomen and the proboscis. Remind students that when the fleas contracted Yersinia pestis, the bacteria clogged the proboscis which caused the fleas to have to bite more frequently to obtain food. When the flea attempts to take a blood meal., it can pass 25,000 to 100,000 bacilli into its victim.

Part 2: Observing Bacteria
The teacher should prepare this activity two days in advance. Safety caution: EMB agar stains--handle very carefully during the powder, liquid, and solid states. Wear goggles when heating and pouring the agar into Petri dishes and when innoculating the agar. Take 36 grams of EMB agar and place it into 1 liter of distilled water and heat to boiling to dissolve completely. This amount should make approximately 12-14 Petri dishes. Sterilize in the autoclave for 15 minutes at 15 pounds pressure. Do not overheat. After autoclaving, gently swirl just prior to pouring contents into sterile Petri dishes. Stagger the innouculation time of the Petri dishes with 1 loop of E. coli so students can visually see the growth of bacteria at different stages. Note: you will want to have at least 6 Petri dishes for each innoculating time. Recommend an innoculation interval time of 2 hours or more. Use a grease pencil and circle on the lid the initial site of innoculation. Students should obtain an appreciation for the exponential growth of bacteria. Teacher should also have 6 permanent slides of E. coli for microscopic viewing.


Vector diseases have been difficult to prevent because you may isolate the bacteria that causes the disease, but you may not immediately identify the vector (transmitter) of the disease. The flea that carried the disease was Xenopsylla cheopis. It carried the bacteria, Yersinia pestis, which was contracted from biting an infected rat, Rattus rattus.

At the beginning of the plague, the disease was spread from rats to rats by fleas. Since rats were found in human dwellings, it was only a matter of time before the fleas began to bite humans. Fleas also contain an excellent internal thermometer which tells them when to leave a dying rat's body. They have an excellent proboscis for blood-sucking, and they can leap so high, that for man to accomplish a comparable leap, he would have to leap over a sixty-story building at the speed of sound!


  1. Discuss the differences between bacteria and viruses.
  2. Discuss the transmission and symptoms of Aids virus.
  3. Discuss the transmission and symptoms of Lyme disease and/or Rocky Mountain Spotted fever.
  4. Contrast bubonic and pneumonic plagues.
  5. Discuss the concept of species specific regarding different species of fleas---explains why all animals did not contract "Black Death".


Busvine, J.R. 1976. Insects, Hygiene, and History. London:Athlone Press.

Dubos, Rene J. 1952. Bacterial and Mycotic Infections of Man. Philadelphia:J.B.Lippincott.

Gregg, Charles T. 1978. Plague-The Shocking Story of a Dread Disease in America Today. New York:Charles Scribner's Sons.

Hendrickson, Robert. 1983. More Cunning Than Man-A Social History of Rats and Men. New York: Stein and Day.

Hull, Thomas G. 1930. Diseases Transmitted from Animals to Man. Baltimore:Charles C. Thomas.

Spink, Wesley W. 1978. Infectious Diseases-Prevention and Treatment in the Nineteenth and Twentieth Centuries. Minneapolis:University of Minnesota Press.

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