Many people have asked if I could tell them something about the history of "third degree" method. Well, the use of physical torture to test a person's innocence was commonly practiced in Europe during medieval times in trial by ordeal. The principle-adapted from pagan rites by the Church-was that a person's innocence in respect of a criminal accusation could be tested by his ability to withstand pain and injury. Two of the most popular tests involved contact with boiling water and red-hot metal. In cases where there was a lack of clear guilt, the accused person was required to plunge his arm into a bowl of scalding water and retrieve a stone! If after 3 days there was evidence of burning on the skin the person was judged to be guilty. Similar tests involved walking on red hot ploughshares or gripping a piece of hot metal in the hands without the flesh being burned. The idea was that if a person was not guilty of the accusation, his innocence would protect him.

So much for the third degree. This time I am going to tell you about a very ingenious way of committing murder. This is by injecting air in somebody's veins. If somebody is indeed murdered using this technique, it is extremely difficult to detect it. Yet there are ways to detect it, if the forensic pathologist is careful. The interesting thing about this sinister technique is that it uses none of the traditional gory weapons like firearms or daggers, nor does it use poisons. The murder device is quite simply and surprisingly air, which is so harmless and ubiquitous. It is almost unbelievable that such an innocuous looking thing as air could kill someone. Actually air or for that matter anything in this universe can kill a person, if it is wrongly placed in a human body. This case is also a similar case. In this case air gets ensconced in a place where it normally shouldn't be! Such cases are technically known as cases of "air embolism". The word embolism comes from Greek en, "in," and ballein, "to throw or cast". Since in this technique, air is "thrown in" or "cast in" the blood vessels, it is known as air embolism. Henceforth we will be using the term "air embolism", whenever we would refer to injection of air in the blood vessels to kill someone. Readers may be interested to know that the concept of air embolism for murder has been used time and again in crime novels, one of the best instances being in the famous writer Dorothy L. Sayer's novel where `a hypodermic of air was injected into an artery'.

Before telling anything further about death by air embolism, let us first understand a little bit about the way our blood circulates in our body. This is very essential to understand how a person get killed by injection of air. Our heart is comprised of 4 chambers. There are two chambers on the right and two on the left side. The chambers on the right side are known as right atrium and right ventricle, while the chambers on the left side are known as left atrium and left ventricle. The location of these chambers will become clearer by referring to the adjacent figure. Here lungs, legs, head and arms are depicted only symbolically. Bad blood from legs, head, arms and in fact from every part of the body returns to the upper right chamber called the right atrium. The bad blood in the figure has been represented by blue colour, while the good blood has been represented by red colour. Keep referring to the figure to follow the route taken by the blood. A proper understanding of the normal route of the blood is very essential.

With each contraction of the heart the right atrium sends this bad blood to the right ventricle. The right ventricle, in turn, sends this blood to the lungs via pulmonary arteries. Do not let the complicated names baffle you. Just remember that atrium and ventricles are fancy sounding names of some chambers of the heart. Ventricle is a larger chamber than atrium. Also keep in mind that "artery" is the name of a conduit which takes the blood away from the heart while vein is the name of a conduit which brings blood to the heart. The word pulmonary comes from Latin pulmo, "the lung". Thus "pulmonary artery" refers to a conduit which takes the blood away from the heart towards the lung.

In the lung, the bad blood is purified. This is done by the help of the air which we breathe all the time (even at the time of sleeping). The pure blood (now depicted as red) is returned to the heart via pulmonary veins. The blood comes in the third chamber of the heart known as left atrium. Left atrium sends this blood to the left ventricle, which in turn, pumps this pure blood to the whole body via a very big conduit known as aorta. The body organs use this pure blood, and when this blood becomes impure, it is once again returned to the right atrium. And thus the circulation goes on.

Now we are ready to understand how air embolism works. First of all we must appreciate that nature has made this whole system of circulation air-proof. This means that there is no way, air could enter this system of conduits and pipes. If somehow air could enter the system (such as by injection of plain air through a syringe), the air will form an "air lock" within the system. This "air lock" is quite familiar to plumbers and owners of diesel engines, where the normal flow of liquid through tubes is wholly or partially blocked by air. Quite in the same manner this air lock blocks the flow of blood through the arteries and veins, thus bringing the circulation to a halt. Let us make this a little more clearer.

Air could be made to enter the circulation either through the arteries (red coloured conduits) or through the veins (blue coloured conduits). More commonly injections for murder are given in the veins. When such an injection is given, the air bubbles start travelling towards the right atrium. From right atrium they keep travelling onwards till they come to the lung. Here the capillaries are too narrow to allow the big bubbles to pass. The result is that these bubbles get entangled in the blood vessels of the lung. The whole blood traffic stops and the person dies very quickly. In fact his bad blood can not be purified by the lungs, because traffic of blood towards the lungs has been stopped. The body can not imagine that such a sinister thing has happened. It "thinks" that the blood is not getting purified because of lack of air. So it quickens the respiration. The person starts gasping. But nothing helps because the cause lies somewhere else and the person dies.

The beauty of the technique lies not only in its simplicity but also in another thing-the difficulty of detection of this condition at post-mortem examination. When a person dies of air embolism, the only abnormal thing that is there within his body is a bubble of air somewhere in his blood vessels. If the forensic pathologist is not careful, the bubble would vanish the moment the body is opened. Thus in every suspected murder case, first of all I take an X-ray of the dead body. It might surprize the reader as to why one would like to X-ray a dead person. The reason is that the air bubbles are seen very well in an X-ray. When the body is still not open, the air bubbles lie undisturbed in the blood vessels and we can see where the bubbles lie. Look at the adjacent figure closely to know where I expect the air bubbles to lie in a case of air-embolism. In the place of lungs you see a network of conduits, which is partly blue coloured and partly red coloured. The air bubbles lie in this network of conduits, and many times in the pulmonary artery itself.

When the X-ray of the dead body indicates that this might indeed be a case of air embolism, we open the body very carefully. Because if we do not open it carefully, the air bubbles might escape the moment the body is opened. In such cases we dissect the blood vessels under water. The detailed technique is very complicated and I do not want to confuse you by giving details of this technique. Just remember that we dissect the blood vessels under water. If air is present within the blood vessels, bubbles of air will be seen to emerge. It is like finding a leak in a bicycle tube by immersing the tube in water!

Murder by air embolism is quite rare, despite the strong chances of a murderer escaping scot free in such cases. This is because such a technique requires great skill. Not everyone can handle a syringe, let alone puncture a vein successfully with it. I have a nagging fear that such type of murder might be very common among the drug addicts of our country. They are quite suited for committing such types of murder. They can handle syringes very deftly (almost as deftly as doctors, as they have to inject the drugs through the syringe all the time), and they need to do away with people fairly commonly.