Phlegm was regarded as important in every system of medicine from ancient times. Blood is tested. Urine and stool are tested. We check or send probes of one sort or another into every part of the body. However, modern medicine seems to me to rather neglect phlegm, at least when it comes to its chemical composition (I should say that I am well aware that phlegm testing is quite common for microbes and other infective agents).
Let me explain my personal background in relation to this.
I have an allergic condition so, for any period when I am affected by it, I produce more than the average quantity of phlegm. As the condition does not last very long (sometimes only a few seconds, sometimes a few minutes, sometimes more), I have not often reflected on the phlegm itself, as my attention of course focuses on reducing the unpleasantness of the situation for myself and others.
But today for the first time it struck me that I should write down my observations and questions regarding phlegm.
First, the phlegm which comes from the first part of the nose has a different constitution from that which is produced by the "back" part of the nasal tract. And that, in turn, is different from the phlegm which is produced by the throat, and that again from the phlegm which is produced by the bronchea. I am not sure how deep into the lungs the apparently-broncheal function of phlegm production goes, or whether the lungs themselves also produce (perhaps minute?) quantities of phlegm that are expelled via the bronchea.
The phlegm expelled by the front of the nose is the lightest, least viscous and least coloured (we could simply say that it is normally the most watery, though that can vary; but the deeper the source of the phlegm, the more likely it is to be heavier and more coloured, depending on whether there is infection in the system, and on how much infection there is in the system).
The above is well known and, in a way, the least interesting thing about phlegm, though that itself might hold some clues, if we were able to answer questions such as: why is some phlegm "heavier"? When and why is phlegm produced in the nose rather than in the throat, or further down the system? What is the connection between phlegm production and bile? Actually, what is its relationship with digestion generally? Because I notice that the allergic production of phlegm at least in my system is connected with these in some way or ways (haven't yet worked out in exactly what way or ways). Is phlegm a way of throwing out poisons that cannot be otherwise eliminated from the system? If so, why? And if so, then chemical analysis of phlegm might be helpful in diagnosing certain medical conditions, not merely bacteriological and viral infections?
The more interesting thing is this: reflecting on the way my own phlegm changes, I notice that my allergic attacks start in the nose (as it were), and then work their way "down" my system. All my allergic attacks move from the phase when my nose is over-reacting, to the stage when my throat is over-reacting (usually for a very short time) to the stage when my bronchea are over-reacting (usually for the longest period of the three, though that might also be relatively short depending on the length of the attack). Of course, this could be merely an individual aberration from the norm. But what is the norm? Is there a norm? Why? (I don't mean of allergies, but I mean of the pattern of phlegm production generally).
Moreover, as the phlegm passes through the system, it creates some sensation in the throat and nose. When the allergic reaction is on any occasion after I have had much dessert (I love desserts) the sensations are more acid. At other times, the sensations may be more salty. Mostly of course the sensation is simply wet. Though sometimes the phlegm can be physically almost hot (certainly at above the temperature of the surrounding tissues). If phlegm is merely mucous consisting of dead cells from the lining of the respiratory tract, infection causing organisms and immune wastes, how come the sensations have this extraordinarily wide range?
In any case, on the basis of these reflections, I recommend to medical researchers to investigate whether adding, to their battery of standard tests, a CHEMICAL biological of phlegm might not be a huge advantage - not only in the diagnosis of diseases to do with the upper respiratory tract but also to do with diseases of the digestive system (and perhaps even the body as a whole - though Western medicine does not seem able to cope with that level of thinking or treatment yet, unlike Ayurvedic, Chinese and other traditional systems of medicine).