Tobacco tar obtained after distillation of tobacco and the same applied on the shaved skin of the mice for some weeks, produced in the skins of only some animals the cancerous changes.
Later, when smoke tar collected under conditions simulating human smoking, and the same was applied on the shaved skin of mice, and the process continued for about their natural life span, changes in the skin somewhat related to lung cancer in human beings, were detected.
When mice were exposed to tobacco smoke in glass vessels and the process was continued for weeks on end, some changes suggestive of leading towards lung cancer could be produced in some.
Experiments were carried out under simulating conditions akin to human smoking. For example, a batch of 24 dogs was taught to inhale smoke by means of tubes inserted directly from their wind pipes into the lungs. Two and a half years later, after having smoked seven cigarettes a day, two of these animals developed lung cancer similar to those of human beings.
Many smokers, by now, know that smoking causes lung cancer, but somehow think, “Its not likely to happen to me”. A victim of such fallacy was one of the eminent doctors, a member of the ten-man commission appointed in 1962, by US Surgeon-General to study and to advise the Government on the health hazards of smoking. While he, with his colleagues, clearly found and stated that cigarette smoking causes lung cancer, he, a chronic smoker, continued smoking. At the age of 66, even though he had cough and breathlessness on exertion, he considered himself in good shape to take up a new assignment. A routine medical check-up, however, revealed a small mass in his lung which on further examination was declared to be lung cancer. Unfortunately for him, it was detected at a very early stage, and was removed by operation. He was saved But in the majority of the smokers who get lung cancer, it is detected and diagnosed at a stage where operation is not possible because of its spread in the surrounding organs or its metastasis in far off organs. The initial symptoms of lung cancer in smokers are not very much different from the usual cough and breathlessness which they may have had for years.
I cannot forget a person whom I had known years before as a man of athletic built, handsome, and with a face radiating life. He came to my clinic, some time ago, and I could hardly recognize him: face pale and puffy, breathless as he entered the room, his finger nails looked to me almost white because of anaemia. His relatives laid before me a bundle of X-rays. It was a case of advanced lung cancer. I thought, he will live at the most, two more months. Later I was informed, that he survived only six weeks. He was 47 then and had been a chronic smoker since the age of 18.
Tobacco and its Smoke:
Tobacco smoke is a gas mixture containing finely divided solid and liquid particles. Under the electron-microscope the major portion of it is found to consist of liquid droplets in the shape of an aerosol. This smoke is said to contain in it about a thousand chemical constituents, of which approximately 270 have been recognized already. The important among them are the nicotine, carbon monoxide gas and a mixture of many chemicals which form, on deposition, a brownish tarry substance commonly called smoke tar.
The active agents in the tar which lead to the production of cancers have been identified as different polycyclic aromatic hydrocarbon compounds.
These are not present initially in the tobacco but are produced as a result of incomplete combustion of tobacco. Roughly about 20 mg of smoke tar passes inside the body of the smoker when he smokes one cigarette. A person who smokes 20 cigarettes a day, thus absorbs about 150 gm of smoke tar in a year. Judging from the effect of its application on laboratory animals, it seems an immense amount to be able to cause serious damage in the lungs.