In connection with a description of the passage of the soul after the death of the body, we are introduced into a new subject, that of the existence of certain psychic nerve currents inside us, known as the nadis. There are certain nadis in our bodies which exist very subtly in the astral layer of our personality and control not only the entire physiological system but also our minds and breathing process - the entire personality. Those who are versed in the science of hatha-yoga will know very well the importance of these nadis.

1. Atha ya eta hrdayasya nadyastah pingalasyanimnas-tisthanti, suklasya nilasya pitasya lohitasyeti. asau va adityah pingalah esa suklah, esa nilah, esa pitah, esa lohitah.

These nerve currents are supposed to be filled with certain subtle juices which are referred to here as animna, very subtle exudation which controls the humours of the body. The point that the Upanishad makes out particularly here is that there is a tremendous connection between the sun and these nerves.

It is not that the sun is spatially very far from us. We have a false notion that the stars in the heaven and the sun in the sky are very far and that they have no connection at all with us here on earth. This intervening space which is the apparent cause for this seeming disconnection is not empty. It is a vital fluid. The ordinary physical notion of the commonplace astronomers that space is not organically connected with the individual has to be given up. In fact, higher aspects of astronomy going into the realm of astrology will tell us that space is not a disconnecting element. If it is, there would be no influence of the planets upon us. They exert a tremendous influence, not merely in a mechanical manner as the law of gravitation does, but in a very, very living and organic manner.

This subtle substance in the nerve currents is of different colours. It may be brownish-yellow, or white, or blue, or yellow proper, or red. These are the types specially mentioned here, though there can be many other permutations and combinations of these colours because we cannot actually count the number of these nerve currents in the system. There are several thousands of nadis, but the principal among them are hundred and one in number. It is believed from the standpoint of this section of the Upanishad that the colours of these nerve currents inside us are due to the influence of the sun upon us. Variegated influences are exerted upon us in respect of the constitution of our personality by the rays of the sun. Even after the sun sets at night, it continues to influence us. The influence of the sun does not cease merely because it is midnight. It is a tremendous influence exerted upon the whole earth. Night and day make no difference for this. When the effect of the sun through its rays has an impact upon the bile in our system, these juices become brownish yellow in colour. When there is phlegmatic element mixed with this bile, it is supposed to be whitish in colour. When the wind element also is included within it, that means to say when the wind humour is a little more predominant, it assumes a blue colour. When there is an equal distribution of the phlegmatic matter and the bile element it becomes yellow, while the reddish element is due to the preponderance of the red corpusles in the blood influencing these juices in the system.

Now, the idea is that the colours of these juices in the nerves are imported, as it were, from the colours in the sun. They are the reflections, as it were, of the sun's rays experienced by us through our own nervous system. So the Upanishad says that these colours are in the sun and they are in the nadis. But what about the causes thereof? These colours - brownish yellow, or white, or blue, or actual yellow, or red-are the colours of the sun's internal structure. We know the sun's rays have colours, and these are responsible for the colours of the juices which flow in the nerve currents.

2. Tad-yatha mahapatha atata ubhau gramau gacchatimam camum ca, evam evaita adityasya rasmaya ubhau lokau gacchantimam camum ca, amusmad-adityat pratayante ta asu uadisu srptah, abhyo nadibhyah pratayante te'musmin aditye srptah.

Just as a national highway passing through villages connects one section of villages on one side to another section on the other side, even so the sun's rays seem to be travelling throughout space like highways, as it were, emanating from the sun, touching the heavens on one side and influencing the individuals and the whole earth on the other side. These rays of the sun are like passages or highways in the entire space. They touch this world and also the other world. They enter even the minutest thing in this world, like X-rays penetrating through objects, and we are not excluded from the influence of these subtle rays of the sun. They penetrate through the nerves inside us, they get refracted back into space and return to the sun, so that they convey a message to the sun, as it were, as to what our predicament is here.

Thus we see there is a real living connection between the sun and ourselves here. The rays are like messengers coming from the sun, conveying to us the message from the sun and taking our message from here and conveying it back to the sun, like postmen. This kind of work the rays of the sun perform much more effectively and vitally than the postal department does! The sun there and ourselves here belong to one family, an undivided family. So, we are like brothers. Most undivided families have division among the members and the undividedness is only an imagination. Really the members of the family are divided. But here the connection is not mere imagination. It is a real interconnection of vital forces in us with the sun and with everything between the sun and ourselves. So we can imagine what integral connection we have really with the atmosphere and the heavens and the stellar system, in spite of our apparently being here as if separated and disconnected. This disconnection is a misconception in our minds.

3. Tad-yatraitat suptah samastah samprasannah svapnam na vijnati asu tada nadisu srpto bhavati tam na kascana papma sprsati, tejasa hi tada sampanno bhavati.

It is these nerve currents that are responsible for the withdrawal of the mind into itself in deep sleep. What we call deep sleep, the composure of the mind, the withdrawal of the mind from all sense activity and the retiring from all dream experience also, where one knows nothing - that experience is brought about by the travel of the various rays of the mind through these nerve currents to the centre of the heart. There the mind then lies sleeping and inactive, doing nothing and knowing nothing. So these nadis have some part to play even in the activity called psychic sleep. In the state of deep sleep we are overpowered by a supernal light.

There are various opinions as to what happens in deep sleep. They differ one from the other. One of the theories is that we fall asleep on account of the fatigue of the senses which results in the exhaustion of the mind searching for happiness in the world. The other doctrine is that the bilious element in our system gets roused up due to the activity of the sun's rays during the day and they make us fatigued in a different way altogether, compelling us to fall asleep. The third theory is that when the mind goes back to its source, it is overwhelmed by the light of the Atman. This getting blinded by that light is in a way equal to seeing nothing. It is seeing darkness, as it were, as perhaps when we gaze at the sun for a long time we see not the brilliance of the sun any more but only pitch darkness. This is a very mystical doctrine of sleep which tells us that we are confronted by the brilliance of the Atman when we go to sleep. And, therefore, on account of there being nothing to see, objectiveness being withdrawn completely, we fall into a mood of so-called unconsciousness, merely because there is nothing for the senses to do and there is nothing for the mind to think. So when there is nothing to sense and nothing to think, what is our condition? It is a falling back into an oblivion of all kinds of experiences.

4. Atha yatraitad-abalimanam nito bhavati, tam abhita asina ahuh janasi mam, janarsi mam, iti, sa yavad asmaccharirad-anutkranto bhavati, tavaj-janati.

Now we are introduced to the principal subject of this section. The other points mentioned in connection with these nerves are introductory to the main point which is the theme of the section, namely the departure of the soul after death.

When a person becomes weak due to old age and is awaiting impending death, people get anxious about his condition. They sit round him thinking that he is about to leave this world. And then they query, "Do you recognise us?", "Do you know I am your father?", "I am so-and-so related to you, do you recognise me?", "Do you know I am your son?", and so on. He is able to reply to these people in a sensible manner as long as the pranas do not depart from the body and as long as the mind is capable of working in a normal fashion in respect of the body. But when the mind is compelled by the pranas to withdraw itself into its source, no sensation, no thought, no recognition remains whatsoever. Then what happens to that person?

5. Atha yatraitad-asmaccharirad-utkramati, athaitair-eva rasmibhir-urdhvam akramate, sa om iti va ha ut va miyate sa yavat ksipyen manah, tavad-adityam gacchati, etad-vai khalu loka-dvaram vidusam prapadanam, nirodho'vidusam.

The very same rays of the sun, about which we have discussed in the earlier mantras in this section, with which we have such an intimate connection, become the passage of the soul for its ascent into the higher regions. These rays of the sun are the roads or the paths, as it were, for the soul when it rises upwards after the departure from this body. This description is in connection with the death of a purified person who is expected to attain liberation by progressive stages, called by the name kramamukti, gradual liberation. Such a person chants Om at the time of death. Everyone will not chant Om at this crucial moment. Those who are accustomed to such a practice throughout life, who have led a very disciplined life of spiritual contemplation throughout their career on earth, will be able to recollect this practice at the time of passing, when usually the mind gets confounded due to the action of natural forces.

How much time does the soul take to jump into the sun? It takes as much time as the mind will take to go to any place. That means it does not take much time. The so-called distance of 93 million miles between the sun up there and the individual here on this earth makes no difference to the soul. It does not take any time at all to reach the sun. Such is the quickness of its action. The soul is taken to the sun at such speed through the passage of the rays. The moment it thinks, it is there. So quickly it is taken there.

This sun is the glorious passage to Brahma-loka, the realm of the Creator. This is the entrance to the glorious immortal abode of Brahma. And also it is the halting and checking place, as it were, for the unknowing persons. Those who do not carry an 'accepted passport' are turned back from the sun. Everyone cannot go there. The knowers go there and the unknowers return. The latter will not even be allowed to touch that spot. So the sun is the check-post where there is a filtering of souls, as it were. The purified ones are allowed to go beyond and the unpurified ones are kicked back to the earth. He is an entrance to the region of Brahma to the purified ones and also a closed door to those who are unprepared for this ascent.

In this connection there is a verse, says the Upanishad.

6. Tad esa slokah:
   satam caika ca hrdayasya nadyah
   tasam murdhanam abhinihsrtaika,
   tayordhvam ayan amrtatvam eti
   visvannya utkramane bhavanti,
   utkramane bhavanti.

One hundred and one are the principal nerve currents in this body. One among these hundred and one moves vertically, as it were, towards the crown of the head. This is usually called the sushumna-nadi in Yogic language. If our prana and minds can travel through this central nerve current called the sushumna and up through the crown of the head, we attain immortality. And this is kramamukti, gradual liberation.

But if the pranas depart not by this central nerve through the crown of the head but through other orifices in the body, then there is rebirth. It may be in this world or it may be in some other lower world, according to the particular passage which the pranas seek at the time of exit. No liberation is possible unless the movement is through sushumna-nadi. So here one part of the discussion of this important subject of the Atman in the heart is concluded.