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Dear Vishi, what's a carcinogen?

Tags: diary letters carcinogen meditation

If you are not living under a cave, you probably have already heard about carcinogens. News is often awash with headlines alerting perils of carcinogens. In a nutshell, these are substances that have the potential to cause cancer. Not all carcinogens cause cancer. Not all cancer is caused by carcinogens. Cancer is a complicated group of diseases. Of course, it’s not my forte to expound on the subject of cancer. However, we should try to understand how carcinogens are identified and what we should do to protect ourselves.

Cancer is pathological mitosis. The cells go bonkers where they have an insatiable urge to proliferate. Carcinogens have the potential to alter the genetic material of the cell. This genetic mutation sometimes can develop into cancer.

How do we know if a substance is a carcinogen or not?

Earlier scientists use to test the substance on animals like rodents for a year or more to see if cancer develops. However, this process is both time-consuming & expensive. Since there a plethora of substances that need to be tested, there was a dire need to cheaply & quickly identify carcinogens.

Bruce Ames developed Ames test. It uses bacteria to test whether a substance can cause mutation. The premise is that mutation often causes cancer. Not all substances that cause mutation are carcinogenic e.g. nitrate compounds gives false positive since they produce nitric oxide. Also, some of the carcinogens may test negative e.g. Nitroethane. Thus Ames test is followed by additional experiments like animal testing to confirm carcinogenicity.

How does the Ames test work?

Let’s say we take a strain of bacteria called Salmonella typhimurium on glucose-minimal salts agar plates. This strain has a mutation that cannot produce histidine (the amino acid is required in biosynthesis). Such bacteria are called auxotrophs since they cannot produce a required nutrient for their growth. This is unlike prototrophs which can synthesize the particular nutrient.


Small traces of histidine present on the plates aids the bacteria grow for several generations until histidine is exhausted, at which time they will stop growing.

Again we repeat the same experiment, but we will also add suspected mutagenic substances on the plates. If the substance is mutagenic, we can see the cluster of bacteria continue to grow even after histidine is exhausted. This is because the bacteria have a mutation that allows them to synthesize histidine.

So Ames test identifies if a substance can cause an auxotroph to revert to prototroph by back-mutation. But remember it has both false positives and false negatives.


Today I meditated for 15 minutes using background music on Youtube. Music aids me in meditation. I know some people prefer to meditate in silence. Do nothing is a difficult concept to grasp for my mind. I guess someday my mind won't wander during meditation. My mind often complains that wandering is not bad. It recites a famous poem

"All that is gold does not glitter,
Not all those who wander are lost;
The old that is strong does not wither,
Deep roots are not reached by the frost" - J.R.R. Tolkien


Today I resumed running on a treadmill. My body becomes lethargic if I skip even a single day. Stamina is something that needs to be built gradually. Below is a snapshot of my activity.

I guess running on a treadmill is the best utilization of the time when India is under lockdown due to Covid-19. In Charlotte, I use to run on a trail. I prefer it more than running on a treadmill. The trail is covered with trees on both sides.

We should feel privileged that we can work from home during this Covid-19 pandemic. A vast number of people probably don’t have that privilege. I am not religiously inclined & don’t prefer dogmas like praying. However, if I had to pray, I would probably chant the following Sanskrit hymn.

सर्वे भवन्तु सुखिनः सर्वे सन्तु निरामया,
सर्वे भद्राणि पश्यन्तु मा कश्चिद् दुख भागभवेत।
ऊँ शान्तिः शान्तिः शान्तिः

This loosely translates as

May all sentient beings be at peace, may no one suffer from illness
May all see what is auspicious, may no one suffer.
Om Peace, peace, peace.

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