Salvarsan 606 – Guiding the Psychopathic Germ Killer
This demonstration was designed to block off access to blind alleys of flawed conceptual understanding when studying Ehrlich’s Salvarsan 606. Pupils seem to struggle with two problems.
Firstly, they could be forgiven for thinking that if this substance could cure disease inside the human body then why was the later development of penicillin so important? True, many texts do publish charts showing that Salvarsan only affected a very narrow range of disease-causing bacterium but these charts appear highly technical and weigh little against the powerful story of Ehrlich’s perseverance and eventual success in the face of a huge task.
Secondly, many pupils do not grasp that Salvarsan was a combination of a dye and a deadly poison. Even those that do are left with the impression of a universally effective killer of bacteria - and this is what they will latch onto with little appreciation as to the dangers of using an arsenic compound inside the body, dangers avoided by the later use of penicillin.
The concept of harnessing and guiding this enduringly lethal substance lends itself to practical demonstration as follows.
Explain to the pupils that the classroom is the human bloodstream and that they each are a bacterium within it. All of them are friendly bacteria with the exception of one. Hand one pupil (of high self esteem and a sense of humour) a sign saying ‘Killer disease bacterium’.
At the front of the room, you don an old T-shirt with ‘psychopathic killer substance’ written or pinned on the front. You could use a football shirt for this if you wish, although the association of football with mindless violence might be a controversial one!
Once you have donned the shirt, act as if you just wish to destroy indiscriminately. Pretend to head butt desks, walls, the board etc and advance towards pupils (not ones of a nervous disposition) saying ‘Right, this one, eh’. Avoid the killer bacterium; concentrate on those pupils who have been told they are ‘friendly bacteria’
Pause for breath. You’ll need to. Discuss with pupils why that substance would be unsuitable to introduce into the bloodstream when most bacteria are friendly. Discuss where the killer substance needs to go – they will quickly say ‘to the killer disease alone’.
Give one gentle pupil a label ‘harmless but clever dye’. Instruct she or he to float around in the class bloodstream identifying the killer bacterium but unable to harm it. A flick with a feather could symbolise this. Now discuss how the ‘harmless but clever dye’ and the ‘psychopathic killer substance’ could work together. Pupils will suggest that the dye could guide the killer substance toward the harmful bacterium.
Resume your psychopathic act but this time get the harmless dye to guide you towards the pupil labelled as ‘Killer disease bacterium’. Pretend to hit this pupil alone with a harmless prop such as an inflatable hammer or baseball bat.
Support with discussion. How ideal was Salvarsan as a cure? Introduce the idea that there are more ‘‘Killer disease bacteria’ that you, as Salvarsan, aren’t interested in attacking. You’re good for dealing with some bacteria but not others. So why were more developments needed?
The concept of the working of Salvarsan as a link between a harmless guiding substance and a deadly indiscriminate killer is now clear. It is seen as an effective but far from ideal cure. The clarification of concept has enabled the later study of penicillin to be done in context.