Important medical discoveries

Learning about important medical discoveries is a crucial aspect of preparing to become a medical student. Understanding the important breakthroughs will help you gain some perspective about how medicine has evolved over the years, and this may give you an idea on how medicine may change over the coming decades. This essay aims to give you an insight on these discoveries, the impact they had and how modern applications of them currently work. It is worth mentioning that this is not a comprehensive list of every significant medical discovery so we urge you not to just utilise this your only tool when looking at medical discoveries, but to also research further to add both breadth and depth to your knowledge of this topic.


In the past, if someone suffered a bacterial infection, it would lead to either their death or amputation of a limb. However, the discovery and therapeutic application of penicillin changed this. In 1928, Alexander Fleming observed that growing Penicillium rubens (a type of fungus) leads to the production of an anti-bacterial substance 1. His discovery occurred when investigating Staphylococcus bacteria and influenza. While growing Staphylococcus on a petri dish, he accidently introduced a fungal spore. Leaving this to incubate for two weeks while on holiday, he found that the fungus had produced a substance that had prevented bacteria to grow 2. He dubbed this “penicillin”.

Howard Florey and a research team furthered Fleming’s work by showing the bactericidal (bacteria killing) action of penicillin and therapeutic studies before devising a way to mass-produce penicillin. In 1945, 7952 billion units of penicillin were produced, relative to the 1633 billion produced in 1944 3. In 1945 Florey, Fleming and Ernst Chain (a member of Florey’s team) shared a Nobel Prize for medicine for their work with penicillin 4.

Penicillin revolutionised the treatment of bacterial infections. It is widely regarded as one of the most essential drugs in the world and was dubbed a “miracle drug” after helping to save many lives during World War II 3. However, we are now facing the consequence of its widespread use: antibiotic resistance. This is when bacteria develop genes that allow them to survive antibiotic treatment – consequently they replicate, causing a widespread infection of the body. Cases of methicillin-resistant Staphylococcus aureus (MRSA) infections have been slowly rising and have the potential to be fatal 5. The pharmaceutical industry will need to invest more time and money into developing new classes of antibiotics to combat these drug-resistant bacteria.

Germ theory

Germ theory states that specific microorganisms are responsible for some diseases 6. The first form of germ theory was produced by Galen and was called the “Miasma Theory”. This theory postulated that “night air” was the cause of multiple diseases including cholera and chlamydia. This would later be rejected in the 1800s, but preceding this, were several important discoveries. Francesco Redi firstly proved that diseases do not occur spontaneously in 1668. He did this by placing meatloaf and an egg in three separate jars – one jar open, one closed and one with a gauze. After a few days he observed that the open jar had maggots inside, while the jar with the gauze only had maggots on the gauze. The closed jar had no maggots at all. From this, he concluded that diseases were not a chance occurence and this was an important first step in developing germ theory 7.

Agostino Bassi then showed that silkworms could be infected by an individual parasite – this was the first time a specific microorganism was identified to cause a disease 8.

In 1876, Robert Koch proved that Anthrax was specifically caused by Bacillus anthracis before creating the four “Koch postulates” 9. These are a set of criteria deemed necessary to determine if a microorganism is the causative agent of a disease, and are as follows:

1. The microorganism or other pathogen must be present in all cases of the disease.
2. The pathogen can be isolated from the diseased host and grown in pure culture.
3. The pathogen from the pure culture must cause the disease when inoculated into a healthy, susceptible laboratory animal.
4. The pathogen must be reisolated from the new host and shown to be the same as the originally inoculated pathogen. 10

Historically, infectious diseases caused by these “germs” were the main cause of death in the world. Since then, developed countries have gained access to clean water and good hygiene practices, consequently preventing the spread of infection – saving numerous lives in the process. However, in developing countries, where there is a lack of adequate hygiene, conditions like cholera still prevail 11. Since concept of the germ theory, Joseph Lister also developed sterile technique – a practical solution to help alleviate the problem of contamination by “germs”. Sterile technique has allowed surgery to become a viable treatment option for many conditions, thus improving the lives of millions around the world 12.


X-Rays were first observed in the 1880s when William Crookes discovered that placing photographic plates near a Crookes tube would cause a form of shadowing – however scientists generally overlooked this at the time 13. Ivan Pulyui found exposure of sealed photographic plates to Crookes tubes lead to them going dark 14. Wilhelm Röntgen however is credited as the person who discovered X-Rays. Initially, he was studying cathode rays and was using a fluorescent screen, when he noticed a green glow emanating from the screen about a metre away. He realised the Crooks tube he was using was most likely producing an invisible ray. He dubbed them “X-Rays” due to their unknown nature 15.
Röntgen systematically studied these unknown rays, and on December 28th 1895, published the first paper on X-Rays. He X-Rayed his wife’s hand and realised their potential for medical application. He was awarded the first Nobel Prize for physics in 1901 16. Thomas Edison then further investigated X-Rays, and found that using a calcium tungstate screen was more fluorescent than barium platinocyanide – which was originally used by Röntgen 17. This is the standard X-Ray screen utilised in modern medical practice. John-Hall Edwards was the first to use X-Rays clinically, and in 1896 he used them to assist with surgical procedures 18.

X-Rays are now the most commonly used form of imaging and are a critically important diagnostic tool. They inform doctors of where bone fractures have occurred and how many pieces of bone there are. Other bone conditions can also be diagnosed too such as osteoarthritis. Even conditions such as heart failure have important diagnostic features that can be visualised on an X Ray. Significant advantages of X-Rays include the ease and speed at which they are performed and its relative cheapness. An important development of the X-Ray is Computed Tomography (CT Scans), which are several cross-sectional 2D X-Ray scans, but when put together can produce a 3D scan. A drawback to using X-Rays is they expose patients and medical professionals to ionising radiation – which could cause cancer. Magnetic Resonance Imagine (MRI) has since been discovered and this does not expose patients to such radiation. However it is used sparingly due to its high expense and the information it provides is different to other imaging techniques 19.


The concept of hereditary diseases had existed for a while, but the biochemical mechanism had eluded scientists thus far, in the past. In 1869 however, Friedrich Miescher isolated a completely novel structure from white blood cells and dubbed this “nuclein”. In 1919 Phoebus Levene, a Russian biochemist, put together a proposed structure of DNA as a “polynucleotide”, correctly deciphering that DNA was comprised of deoxyribose, phosphate and one of 4 nitrogen-containing bases. However, his structure was oversimplified, and thought bases ran in just one order as opposed to being completely variable20.

Erwin Chargaff built upon Levene’s work and in 1950, he had two important observations. The first was that base order can be completely varied – something Levene failed to recognise in his polynucleotide structure. The second observation he made was that the number of adenine and thymine bases were similar, and the number of guanine and cytosine bases were similar i.e. the number of purine bases = the number of pyrimidine bases as adenine and guanine are purine, while thymine and cytosine are pyrimidine. This is known as Chargaff’s rule 20.

Francis Crick, James Watson, Maurice Wilkins and Rosalind Franklin subsequently built upon this work in 1953 – to discover the DNA structure we know today. They acknowledged that thymine binds to adenine, and guanine binds to cytosine – and that they are held together by hydrogen bonds. They discovered that the strands of DNA are in a helix and are anti-parallel i.e. the two strands run in opposing directions to each other 20. Crick, Watson and Wilkins were all awarded Nobel prizes in 1962 for their work 21.

Consequently, a completely new aspect to heritability had been discovered. Scientists were now able to use molecules to prove that genes could be passed down between generations – and this had several clinical implications. Medical genetics is a specialty pertaining to heritable diseases and specialists in this field play a role in providing genetic counselling for patients diagnosed with such conditions. Novel techniques such as gene chips were developed to assist with diagnosis of genetic diseases. The discovery of DNA has also vastly improved cancer research and treatment. Isolation of important genetic mutations which predisposes people to cancer allows doctors to identify those at risk before taking preventative actions (e.g. mastectomies) 22.

Medical research techniques have also improved vastly, thanks to this discovery. The Human Genome Project was created in 1984 and was completed in 2003. Its aim was to determine the sequence base pairs of each part of our DNA, and map out the physical and functional nature of our genome 23. We can now genetically engineer proteins by utilising plasmids as vectors and try out various experiments. We can knock out genes and see what happens if mutations occur in them 24. The discovery of DNA has revolutionised how we look at both medicine and research.


“Prevention of the disease is better than the cure” is an important principle in medicine and is exemplified by the introduction of vaccines. The first vaccine developed was for smallpox, and was introduced in 1798 by Edward Jenner. A horrifying infectious disease, smallpox lead to the deaths of an estimated 300 million in the 20th century 25 26. The vaccination was utilised worldwide and in 1980, smallpox was considered to be completely eradicated 27.

Since the smallpox vaccine was created, vaccinations have been produced for a multitude of infectious diseases. This includes vaccines against polio, mumps, measles, rubella, diptheria and tetanus amongst many more 28. Vaccinations are administered to babies and children, who have a poor immune system and are thus more susceptible to infection. Vaccinations have proved to be an effective tool in preventing infectious diseases. In communities where the majority of people are vaccinated, herd immunity can be developed with mass vaccination. Disease outbreaks such as that of smallpox, are now very rare 29.

An important side note here should be added regarding the negative media coverage surrounding vaccinations is that currently there is no scientific evidence linking their administration to autism 30. This myth was first postulated when Andrew Wakefield published a paper linking the MMR (measles, mumps and rubella) vaccine to autism in The Lancet in 1998. However, the study had very clear limitations and the results had been falsified. Subsequently, the paper was retracted and Wakefield was struck off the GMC but unfortunately his legacy has lived on 31. The anti-vaccination campaign has so far lead to death of over 9000 people between June 3rd 2007 and May 9th 2015 and has undermined one of the most important medical developments in history 32.

Stem Cells

Stem cells were first mentioned in 1868 when Ernst Heckel discussed the development of a single-cell fertilised egg into a multicellular organism 33. In 1909, Alexander Maximow postulated that all blood cells came from a common ancestor cell – this was the first theory of how cells differentiate 33. E. Donnall Thomas then attempted a bone marrow transplant in 1957 – subsequently winning a Nobel prize in 1990 for this work 33 34. Ernest McCulloch and James Till, two Canadian scientists, observed that different blood cells come from a single lineage in 1963. This was published in Nature and was the first piece of evidence proving stem cells existed 35. Martin Evans and Gail Martin conducted two separate studies and were the first to isolate embryonic stem cells in 1981 33. Andrew Lassar, Bruce Paterson, and Harold Weintraub successfully converted a fibroblast into a myoblast in 1986. Being able to convert one type of cell into another is a crucial aspect of regenerative medicine and this has yielded some fruit within the research field 36. In 2005, South Korean scientists claimed to have cloned human stem cells (previously the majority of studies were performed on mice) however these results were found to be falsified 37. In 2006 stem cells were found to be inducible – this has the potential to be important clinically as it would allow us to “reprogram” defective cells and this is a current focus of research 38.

Since their discovery, stem cells have revolutionised the clinical treatment of many conditions. Bone marrow transplants have vastly improved treatment options for those suffering from leukaemia, non-Hodgkin lymphoma and certain types of anaemia 39. They offer a more successful solution to treating these complex diseases and they may even offer complete cures once further researched 40. The hope for the future is that stem cells can be manipulated to produce new organs. Type 1 diabetes mellitus and heart failure are currently two vast areas of research which scientists are focusing on, but any damaged organ has the potential to be replaced 41 42. The discovery of stem cells has had huge implications within the research world as well. Recently, neuroscientists utilised stem cells to model brain development – this is important as one can see how altering development leads to different pathologies. Stem cells are potentially the solution to our rising incidence of non-communicable diseases 43.
It is worth highlighting that the utilisation of stem cells and their research is a hugely controversial topic. Concerns about their research leading to human cloning have lead to numerous debates. Other ethical dilemmas pertain to the moral status of embryos. Such issues led to then President of the United States, George Bush hugely reducing stem cell research funding in 2001. He then vetoed a bill trying to scrap the ban on federal spending on stem cells in 2006 44. President Barack Obama managed to scrap the federal spending ban stating, “miracles don’t happen by accident” and referring to their potential usefulness as the reason 45.

Charles Hull was responsible for a revolutionary idea within the manufacturing industry. His invention ‘stereolithography’ (more commonly known as 3D printing) was completed by 1983. He subsequently founded his company ‘3D Systems’ in 1986, which was dedicated to improving stereolithography. They developed software compatible with 3D printing to ensure it became a viable industrial tool. While initially starting off with plastic, metal is now a material that can be printed 46 47. Bioengineering techniques have since incorporated the ability to manipulate human tissue cells, thanks to 3D printing 48.

3-Dimensional (3D) printing has been an exciting new development in the technological field. While its initial purpose was for manufacturing, its application extends to the medical field. 3D printing allows for mass production of tablets containing drugs – allowing companies to make huge savings, with the hope of this translating into lower prices for consumers 49. In 2014, the first prosthetic hand was designed and 3D printed followed by successful implantation into a child 50. Complex structures such as organs will hopefully be available in the future. The hope amongst medics is that 3D technology will improve the efficiency of producing various medical paraphernalia to help reduce costs of providing these products.

Overall, this essay illustrates how medical discoveries have impacted practice over time. An important factor one must bear in mind when considering these is the context of these discoveries. The reason these were so revolutionary is that they solved huge problems during their time. For example, in the early 1900s people tended to die from infections – and this is why penicillin, vaccines and germ theory were so vital in preventing and curing these deaths. Now we have moved into a different era where non-communicable diseases seem to be more prevalent. Cancer incidence appears to be rising and conditions such as heart failure and dementia are becoming more common. Discoveries relating to DNA and stem cells may yield fruit in the future clinically. While this essay is informative, one should question the world at the time, and consider the world currently and how medicine needs to further evolve to improve people’s lives.


1 Houbraken J, Frisvad J, Samson R. Fleming’s penicillin producing strain is not Penicillium chrysogenum but P. rubens. IMA Fungus. 2011;2(1):87-95.

2 BBC – History – Alexander Fleming [Internet]. 2014 [cited 12 September 2015]. Available from:

3 Penicillin: Medicine’s Wartime Wonder Drug and Its Production at Peoria, Illinois [Internet]. [cited 15 September 2015]. Available from:

4 The Nobel Prize in Physiology or Medicine 1945 [Internet]. 2014 [cited 15 September 2015]. Available from:

5 Boucher H, Corey G. Epidemiology of Methicillin‐Resistant Staphylococcus aureus. Clinical Infectious Diseases. 2008;46(S5):S344-S349.

6 Germ Theory [Internet]. [cited 15 September 2015]. Available from:

7 Karamanou M, Panayiotakopoulos G, Tsoucalas G, Kousoulis A, Androutsos G. Dai miasmi ai germi: un approccio storiografico alle teorie della trasmissione delle malattie infettive. Le Infezioni in Medicina [Internet]. 2012 [cited 15 September 2015];20(1):58-62. Available from:

8 Baldry P. The battle against bacteria. 3rd ed. Cambridge [England]: Cambridge University Press; 1976.

9 Robert Koch (1843-1910) [Internet]. 2015 [cited 15 September 2015]. Available from:

10 Koch’s Postulates [Internet]. [cited 15 September 2015]. Available from:

11 Msyamboza K, Kagoli M, M’bang’ombe M, Chipeta S, Masuku H. Cholera outbreaks in Malawi in 1998-2012: social and cultural challenges in prevention and control. J Infect Dev Ctries. 2014;8(06).

12 Joseph Lister and antiseptic surgery – ABPI – Resources for Schools [Internet]. [cited 15 September 2015]. Available from:

13 The Cathode Ray Tube site, X-Ray tubes. [Internet]. [cited 17 September 2015]. Available from:

14 Oradect. Introduction to Digital X-ray | OraDect [Internet]. [cited 17 September 2015]. Available from:

15 Rays and Particles [Internet]. [cited 17 September 2015]. Available from:

16 The Nobel Prize in Physics 1901 – Perspectives [Internet]. 2014 [cited 17 September 2015]. Available from:

17 EHS – Radiation Safety – Resources & Links – Historical Figures [Internet]. [cited 17 September 2015]. Available from:

18 Major John Hall-Edwards – Birmingham City Council [Internet]. [cited 17 September 2015]. Available from:

19 Daffner R. Clinical radiology. 3rd ed. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins; 2007.

20 Pray L. Discovery of DNA Structure and Function: Watson and Crick. Nature Education. 2008;1(1).

21 The Nobel Prize in Physiology or Medicine 1962 [Internet]. 2014 [cited 17 September 2015]. Available from:

22 Young I. Medical genetics. Oxford: Oxford University Press; 2005.

23 An Overview of the Human Genome Project [Internet]. 2015 [cited 17 September 2015]. Available from:

24 Trent R. Molecular medicine. 3rd ed. Amsterdam: Elsevier Academic Press; 2005.

25 CDC Smallpox | Smallpox Overview [Internet]. [cited 17 September 2015]. Available from:

26 UC Davis Magazine, Summer 2006: Epidemics on the Horizon [Internet]. 2006 [cited 17 September 2015]. Available from:

27 WHO | Smallpox [Internet]. [cited 17 September 2015]. Available from:

28 Vaccination schedule – Vaccinations – NHS Choices [Internet]. [cited 17 September 2015]. Available from:

29 Abbas A, Lichtman A, Pillai S. Cellular and molecular immunology. 7th ed. Philadelphia: Elsevier/Saunders; 2012.

30 Taylor L, Swerdfeger A, Eslick G. Vaccines are not associated with autism: An evidence-based meta-analysis of case-control and cohort studies. Vaccine. 2014;32(29):3623-3629.

31 Godlee F, Smith J, Marcovitch H. Wakefield’s article linking MMR vaccine and autism was fraudulent. BMJ. 2011;342(jan05 1):c7452-c7452.

32 Anti-Vaccine Body Count [Internet]. [cited 17 September 2015]. Available from:

33 History | Boston Children’s Hospital [Internet]. [cited 30 September 2015]. Available from:

34 The Nobel Prize in Physiology or Medicine 1990 [Internet]. 2014 [cited 30 September 2015]. Available from:

35 BECKER A, McCULLOCH E, TILL J. Cytological Demonstration of the Clonal Nature of Spleen Colonies Derived from Transplanted Mouse Marrow Cells. Nature. 1963;197(4866):452-454.

36 Lassar A, Paterson B, Weintraub H. Transfection of a DNA locus that mediates the conversion of 10T12 fibroblasts to myoblasts. Cell. 1986;47(5):649-656.

37 BBC NEWS | Asia-Pacific | S Korea cloning research was fake [Internet]. 2005 [cited 30 September 2015]. Available from:

38 Takahashi K, Yamanaka S. Induction of Pluripotent Stem Cells from Mouse Embryonic and Adult Fibroblast Cultures by Defined Factors. Cell. 2006;126(4):663-676.

39 Bone marrow transplant – NHS Choices [Internet]. [cited 30 September 2015]. Available from:

40 Bone marrow transplants | Cancer Research UK [Internet]. [cited 30 September 2015]. Available from:

41 Chong J, Yang X, Don C, Minami E, Liu Y, Weyers J et al. Human embryonic-stem-cell-derived cardiomyocytes regenerate non-human primate hearts. Nature. 2014;510(7504):273-277.

42 From stem cells to billions of human insulin-producing cells [Internet]. 2014 [cited 30 September 2015]. Available from:

43 Lancaster M, Renner M, Martin C, Wenzel D, Bicknell L, Hurles M et al. Cerebral organoids model human brain development and microcephaly. Nature. 2013;501(7467):373-379.

44 BBC NEWS | Americas | Bush uses veto on stem cell bill [Internet]. 2006 [cited 30 September 2015]. Available from:

45 Obama Ends Stem Cell Research Ban [Internet]. 2015 [cited 30 September 2015]. Available from:

46 3D Systems. 30 Years of Innovation [Internet]. [cited 30 September 2015]. Available from:

47 3D Printing Industry. 3D Printing History: The Free Beginner’s Guide – 3D Printing Industry [Internet]. [cited 30 September 2015]. Available from:

48 3DPrinting: Bioprinting organs/human tissue cells [Internet]. [cited 30 September 2015]. Available from:

49 Palmer E. Company builds plant for 3DP pill making as it nails first FDA approval [Internet]. FiercePharmaManufacturing. 2015 [cited 30 September 2015]. Available from:

50 BBC News. Inverness girl Hayley Fraser gets 3D-printed hand – BBC News [Internet]. 2014 [cited 30 September 2015]. Available from:

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