Yage is a drug made from a plant of the same name found in the Amazon rainforest.   Shaman have used this drug for years to put themselves into trances.   They have found out that anyone under the influence of this drug can communicate telepathically with other users of this drug.   CHESS has cultivated Yage as a means of communication.   At any time, there are a few CHESS agents chewing Yage.  This means that any feild agent can use their issued Yage as a means to request help,  give information or recieve information.   One must be trained on how to use Yage or one can become confused or even incapacitated. 
    The link created by Yage users is called Interzone.  Unfortunatly, anyone with access to Yage, also has access to Interzone.   This is why CHESS tries to keep Yage out of anyone else's hands.

As and act of desperation, Doctor Anton Borgia is going to inject himself, along with his patient,  Phillip Manning, with yage.  He hope to create a telepathic link with the comatose man as a way to learn how to treat him.