U Ba Khin and his reference to Parajikan Atthakatha

U Ba Khin, in IMC: Personal Experiences of Candidates , writes some quite interesting "explanatory remarks" about the experiences that Mr. J. Van Amersfoort had during a meditation course. In those remarks U Ba Khin sees the **Parajikan Atthakatha** as an authoritative treatise which talks about the "*realization of the Truth by an analysis of the kalapas in the body with the lens of Samadhi obtained through Anapana Sati*". I was not able to find the text of that Parajikan Atthakatha, as far I could gather it should be a Vinaya commentary. Does someone have a full English translation of it? I would be interested in how it deals with kalapas.