P. V. Kane cites a line from the Santiparva of the Mahabharata while examining the question whether the former "untouchables" were comprised, within the sudra varna This note questions his use of the line and demonstrates how it radically challenges prevalent notions of the sudra in classical Hinduism when read contra Kane, in context.
P. V. Kane's erudition as a scholar of dharmasastra is beyond hyperbole. But to err is human. I would like to draw the attention of the scholarly world to one such lapse through this note, especially as it is not inconsequential. It involves questions of both probative value and prejudicial impact.
The context is provided by the question: do "untouchables" (now Dalits) belong to the category of sudra? Our difficulty does not lie with the affirmative answer offered by P. V. Kane, in general. It lies with his use of the evidence provided by a line from the Santiparva of the Mahabharata, in particular. Kane argues that the word-vaidehika refers to an "untouchable" and "because the Santiparva 297.28 expressly says that the vaidehika is called sudra by learned dvijas,"  it is clear that "untouchables" are comprised within the sudra class. The Sanskrit text cited is as follows: vaidehikam sudram udaharanti dvija maharaja srutopapannah. 
The relevant line seems to have been misconstrued by P. V. Kane, and by employing it the way he does, he virtually reverses its purport--a purport in some ways unique in the annals of Hindu social history.
Kane interprets the line to mean that "the vaidehika is called sudra by learned dvijas." This is certainly one way in which the line could be read by itself, as the word vaidehaka (= vaidehika) has been used elsewhere to denote an "untouchable." 
The line, however, does not stand by itself. It constitutes the first line of a stanza of four lines. This stanza occurs, with some variations, in all the readily accessible texts of the Mahabharata. It appears along with two variant readings of the first line, as follows:
vaidehikam sudram udaharanti dvija maharaja srutopapannah aham hi pasyami narendra devam visvasya visnum jagatah pradhanam 
(1) vaidehakam sudram udaharanti 
(2) vaideha kam sudram udaharanti 
P. H. Prabhu translates the verse, in the reading he shares with P. V. Kane, as follows:
Brahmanas learned in the Vedas regard a-virtuous Sudra as a model of a Brahmana himself. I, however, regard such a Sudra as the effulgent Vishnu of the universe, the...