ANSWERS TO TEXT BOOK SPU MODULE 1
CHAPTER 1
1 There is no simple answer. Scientific developments can always be traced to a range of factors, both social and technological. Some of the factors which contributed to the germ theory at this time are as follows:-
• understanding of cells as the unit of living organisms, mainly as a result of botany and the use of microscopes.
• the decline of religion and its belief that everything that happened to humans, including infection, was a result of God’s will.
• improvements in technology such as better microscopes.
• science was becoming a significant part of the culture and the success of scientific explanations in other branches of science would have encouraged investigation.
2 Infection occurs when germs are transmitted from an infected patient to others. When patients are in close contact, as in a hospital, this is more likely. Medical staff moving between patients would carry the germs unless they take precautions. In home deliveries there would be very little chance of contact between one mother and another so any infection is less likely to spread.
3 The germ theory is very much part of our culture. It influences how our parents teach us to behave long before we understand the science. It is therefore quite hard for us to analyse which of our actions are determined by our belief in the germ theory. Some of these actions would include, sneezing into a handkerchief, washing our hands before eating or preparing food, not eating spoiled food. There are many others.
4 The factors, in the order in which Semmelweiss considered them, were:-
• medical students seemed more likely to cause the disease than midwives,
•the main difference between these two groups of carers was that medical students also dissected corpses,
•an infectious agent found in corpses might be transmitted to patients through cuts
•the role of hand-washing in preventing infection.
Semmelweiss found that the more careful and frequent the doctors’ hand-washing the less the infection of mothers.
5 Semmelweiss showed that if new mothers were protected from contact with material from an infected mother or from a corpse they were much less likely to become infected with puerperal fever. This discovery is consistent with germ theory but he was not able to identify what this material was, so he did not actually discover germs.
6 Chlorinated lime is an effective disinfectant, it kills the germs carried on the doctors’ hands.
7 Hand washing before eating, before preparing food, after using toilet. Washing fruit and vegetables.
Keeping food cold. Keeping food covered.
8 Semmelweiss was young and inexperienced. He was proposing a significant change in accepted practice. People seldom change their minds easily unless they have enormous respect for the person suggesting the change. Scientific evidence alone is very slow to change ideas. Semmelweiss’s experience is in contrast with the rapid acceptance of Pasteur’s ideas 10 or 15 years later because
Pasteur’s reputation had already been established.
9 Preventive measures are very effective in reducing the incidence of infectious diseases such as puerperal fever. However there is almost always a need for curative measures as well, to treat the few cases which still occur. Antibiotics, the only cure for puerperal fever, were only introduced in the 1950s.
Until then a few women continued to die.
10 In developing countries many women give birth at home, assisted by a traditional birth attendant. They have very little clean water so even if they understand the importance of hygiene it is difficult to achieve. But also many people who have had little or no education still use traditional practices, which may actually introduce infection. Instruments are not sterilised, local materials such as dung or plant material may be applied to the woman. In many areas the nearest medical services may be too far away.
Education and training for local traditional midwives is probably the most important way of preventing these deaths. But the midwives also need more access to sterile equipment, antibiotics and clean water as well as support from medically qualified staff if there are complications.
Answers which suggest that all women should give birth in modern hospitals, attended by qualified doctors are not acceptable. They reflect a lack of awareness of the reality of life in the rural areas of developing countries.

11 Lack of either sanitation or rubbish disposal made the air smell bad. This led to the theory that the bad smells given off by any decomposing organic matter or rotten flesh could cause disease. The theory explained the well known association between unhygienic living conditions, and rates of infection.
12 Burning tar smells strongly and might be thought to counteract the miasma smells. Whitewash would make things look cleaner.
13 Chadwick believed that the smells in the air caused the disease. He therefore predicted that reducing smells by removing sewage would reduce disease. However by washing all infected sewage into the
Thames he actually spread cholera because at that time many people all over London used water taken directly from the Thames. Drinking infected water is a very effective way of catching cholera.
14 If the infectious agent multiplied in an infected person it would explain how the disease developed in the individual. But even more important, it explained how one infected person could supply enough material to infect a large number of other people.
15 Snow showed clearly that there was a correlation between the water supply and the incidence of cholera. He was not able to demonstrate a causative agent actually in the water. He was not believed because people were unwilling to believe in germs that they could not see, smell or taste. They wanted more evidence before overthrowing an existing theory.
16 Snow’s theory:- cholera enters the body through the digestive system cholera is transmitted by water and direct contact it is caused by a germ which multiplies in the infected person the germs are excreted in the faeces of an ill person it is contamination of the water supply by this sewage which spreads the disease.
17 It was public. It worked. It was easy to understand.
18 The two conflicting theories led to two different, testable, predictions for the probable distribution of cholera cases in the area. In part of South London houses in the same street often got water from different suppliers. One of the suppliers provided clean unpolluted water, the other provided Thames water containing sewage. The miasma theory would predict that people living in the same street would breathe the same air and therefore have the same chance of getting cholera. The water-borne theory would predict that the chance of getting cholera depended on the water supply not the air in that street.
Snow found that the incidence of cholera was linked to the water supply, as predicted by his theory, but not by the miasma theory.
19 Although all his evidence pointed to a germ, transmitted in water, as the cause of cholera he was unable to actually show the germs. It is usually essential to demonstrate the causal agent and a mechanism before a theory can be fully accepted.
20 The two men were working at almost the same time and the methods and knowledge available to them were very similar. Some of the similarities are listed below.
Because they were concerned about a high death rate from a particular disease both started to make careful observations in the course of their normal clinical work.
Both identified connections between disease and other factors which had been missed by their colleagues.
Both were able to use controls in their investigations - Semmelweiss in the two wards with different medical staff, Snow in the houses receiving water from different sources.
They both used imagination in suggesting the existence of infectious particles which could not be seen.
Both, not only studied the science, but also did what they could to apply their ideas to prevention of disease.
Snow’s theory was probably the more fully developed in that he wrote about the replication of the germs in the body. Snow used detailed surveys and epidemiology more extensively than Semmelweiss.
21 Death from any disease may be due to a failure of either prevention or cure.
The most important methods for prevention of cholera are the provision of clean water and effective sewage treatment and disposal. In Low Income countries neither of these measures are widely available so once one person is infected the disease is able to spread rapidly. This is a particular problem when people are crowded together as they are in refugee camps.
Death from cholera is due to dehydration rather than the toxicity of the bacteria and it is often possible to cure the patient if they drink large quantities of clean water containing salts and sugar. Nowadays health workers are all taught about the importance of this Oral Rehydration but not everyone who gets cholera is cared for by someone with this knowledge.
Children are particularly vulnerable because their immune systems are less developed. They may also take less hygiene precautions.
22 It is not possible to test every situation and therefore it is always possible that some unexpected factor could cause spontaneous generation.
2

Pasteur set out to show that it does not happen under any of the conditions he tested. He then made the generalisation that spontaneous generation is not possible. But all such scientific theories are provisional, they might be changed by new discoveries.
23 The short answer is that it is easier to believe in germs once you can actually see them. Good microscopes allow you to recognise differences between different organisms and to learn that the organism is specific to the particular disease.
The longer answer would require an explanation of Koch’s work. Experimental work based on his postulates finally confirmed the germ theory of disease.
24 Bacteria start reproducing as soon as they enter the body and multiply at a steady rate by cell division.
As the number of bacteria in the body increases the symptoms become worse.
A virus has to enter a cell in the body and use the mechanisms of the cell to reproduce. Whilst the viruses are growing inside cells there will be very few symptoms. Once the cell is full of viruses it bursts. The symptoms of the illness are usually caused by this sudden cell damage. The viruses go on to invade new cells and the symptoms subside until the next wave of cells burst.
25 Semmelwiess observed that childbed fever was spread by doctors or medical students going directly from one patient to another or from the dissecting room to the patients. The medical students did not become ill but a doctor died from the same symptoms after cutting himself during dissection. The explanation for these observations is that the germs from a corpse or an infected person can be transmitted by contact but only enter the body through cuts or wounds, common during childbirth.
Snow observed that cholera infection seemed to be spread by contaminated water. The explanation is that the bacteria are excreted in the diarrhoea of a sick person. If this is allowed to contaminate drinking water then the bacteria will be swallowed and may cause infection.
26 When hygiene is poor the air smells bad and people are more likely to get cholera. There is a correlation between bad smell and cholera, which could lead people to believe that one caused the other. In fact, of course, the correlation exists because they both have a common cause, the poor hygiene.
It is well known that when people are in close contact with an ill person they are more likely to catch the disease themselves. Close contact means that they may both touch the patient and breathe in germcontaining droplets from nasal spray or coughs. Because the germ-containing droplets are not visible people assumed that it was the touch that transmitted the disease. In fact diseases are rarely transmitted by touch unless the skin is broken.
27 The most straightforward way of showing the causal link would be to devise an experiment whereby some people were exposed to the disease by the proposed method of transmission and to then compare their rate of infection with that of a control group. However in most cases this would be totally unethical. This technique could be used on animals if there is a species which is susceptible to the same disease.
The other important method used is to isolate the infectious organism, to identify this organism in the ill person in every case of the disease and also in the transmission route. The discovery of the malaria trypanosomes inside mosquitoes as well as in malaria patients was a vital step in understanding the transmission of malaria .
To show that Staphylococcus infections are transmitted in hospital bedding it would be necessary to find the same strain of bacterium in the bedding as in the patient. This by itself might be due to common cause and it would also be necessary to show that killing the bacteria in the sheets reduced the transmission rate to patients.
28 The only single conclusive method is to introduce the bacteria into the healthy stomachs of several people and show that they go on to develop ulcers. There should also be a control group who have the same diet and life-style but do not receive the bacteria. However the use of humans as experimental subjects in this way is not ethically acceptable.
Marshall showed that Helicobacter could always be found in the stomach of patients with ulcers and that when the bacterial infection was cured with antibiotics the ulcers healed too. Other treatments for ulcers alleviated the symptoms but they always recurred. Over about 10 years other doctors have repeated Marshall’s work and now most accept the hypothesis.This case shows that a change of theory may not be due to one conclusive experiment but often comes about as evidence gradually builds up and more and more people come to change their minds.
29 People are generally quite reluctant to change their minds, especially if, as in this case, their professional status is linked to the knowledge being challenged. The idea that bacteria could exist in the acid conditions of the stomach also contradicted accepted knowledge about the digestive system.
Researchers were unable to show the causal connection directly using animal experiments because, until very recently, no one had found an animal which developed stomach ulcers.
3

As a chronic condition ulcers require regular treatment. If a doctor’s practice depended on such work they might also be reluctant to accept that they would no longer be needed. Some doctors could put their own needs before those of their patients in this way.
Drug companies spent millions and millions of pounds developing drugs to treat ulcers and were making excellent profits. It is possible that these companies did nothing to support acceptance of the theory.
30 There was no alternative effective treatment of stomach cancer so there was a greater readiness to accept any possible treatment.
Marshall had a reputation as a result of his successful work on ulcers so was taken more seriously.
31 Data Semmelweiss’s records on death rates in the labour wards
Snow’s records in Broad St or in Lambeth
Koch’s observations and identification of bacteria
(Note that these observations were not random, the scientist had some idea of what sort of data it might be significant to collect.)
Evidence Semmelweiss’s records of the effects of hand-washing on death rates are evidence which supports his hypothesis.
Snow’s records similarly support his hypothesis.
Patterns Snow did not just collect data he realised that there was a pattern of cholera deaths associated with the water supply.
Marshall noticed a pattern of the association between the presence of Helicobacter and ulcers.
Generalisations Having cured some stomach ulcers with antibiotics, Marshall proposed the generalisation that all such ulcers are caused by the helicobacter.
Explanation The germ theory of disease is an explanation. It explains many of the observations above, including the transmission of cholera, Pasteur’s flasks and the importance of hygiene. It leads to the testable prediction that it would be possible to isolate specific germs from patients with specific diseases. Koch was the first scientist to do this successfully.
32 The time line below includes more examples that are expected from the information in this chapter. It
Year includes information to be found in later chapters.
Scientist Development
1796 Jenner Demonstrated the use of cow-pox as a safe effective vaccine against smallpox
1840 Henle
1847
1849
Ignaz
Semmelweiss
John Snow
1854
1854
1856
1861
Florence
Nightingale
John Snow
Louis Pasteur
Louis Pasteur
Suggested that micro-parasites cause fermentation, putrefaction and disease
Showed that hand-washing by medical staff reduced the incidence of puerperal fever
First published his hypothesis on infected water as the route of transmission of cholera
Insisted on cleanliness in hospitals
Showed evidence of the correlation between water supply and cholera which strongly supported his hypothesis
Demonstrated that yeast is essential for fermentation
Refuted spontaneous generation using his swan-necked flasks
4

1865 Joseph Lister
1879 Robert Koch
1881 Pasteur
1882 Robert Koch
Used antiseptics to reduce deaths after surgery
Isolated a bacillus and showed that it caused anthrax
Demonstrated an anthrax vaccine in sheep
Discovered the TB bacillus
1885 Pasteur
1909 Paul Ehrlich
Carried out the first human trial of rabies vaccine in a child
Developed the first specific antibacterial drug
1928
1921
Alexander
Fleming
Discovered penicillin
BCG vaccine against TB produced
The first virus isolated 1935
33 All the authorities whom we trust support germ theory and the theory seems to be confirmed by all the evidence available to us.
We no longer believe a God who sends punishments but humans always want some explanation for events in their lives.
Belief in the theory allows us to use antibiotics to cure many diseases.
This is related to our attitude to risk. Although we do believe in germ theory we know that it is not possible to eliminate all germs from our bodies. We decide what level of risk is acceptable to us. In the case of food we may simply decide that the convenience or pleasure we gain from these foods outweighs the, not very high, risk. We make these kinds of personal choices over many risky activities, such as smoking.
34 They are seldom mentioned because the germ theory has been so successful in terms of explanations and predictions. There is no longer any doubt in the minds of almost all those involved that it is correct.
A single experiment does not overthrow a successful widely accepted theory. There are counterexamples for most theories, mostly treated as “the experiment that did not work”. Any experiment which gave results as unexpected as this would have to be repeated many times very carefully before it was taken seriously. It is likely that these people were lucky enough to be particularly resistant to cholera, maybe because their stomachs were unusually acidic.
5