The caste system, though it may be slowly yielding in non-essentials to the exigencies of modern life, is still vigorous to-day in all its essential features, and cannot easily be extruded from their family life even by the Western-educated classes.  It divides up Indian society into thousands of water-tight compartments within which the Hindu is born and lives and dies without any possibility of emerging from the one to which he has been predestined by his own deeds in his former lives.  Each caste forms a group, of which the relations within its own circle, as well as with other groups, are governed by the most rigid laws—­in no connection more rigid than in regard to marriage.  These groups are of many different types; some are of the tribal type, some national, some sectarian, some have been formed by migration, some are based upon a common social function or occupation past or present, some on peculiarities of religious beliefs and superstitions.  A distinguished French writer, M. Senart, has described a caste as a close corporation, in theory at any rate rigorously hereditary, equipped with a certain traditional and independent organisation, observing certain common usages, more particularly as to marriage, food, and questions of ceremonial pollution, and ruling its members by the sanction of certain penalties of which the most signal is the sentence of irrevocable exclusion or out-casting.  The Census of 1901 was the first to attempt a thorough classification of Indian castes, and the number of the main castes enumerated in it is well over two thousand, each one divided up again into almost endless sub-castes.  The keystone of the whole caste system is the supremacy of the quasi-sacerdotal caste of Brahmans—­a caste which constitutes in some respects the proudest and closest aristocracy that the world has ever seen, since it is not merely an aristocracy of birth in the strictest sense of the term, but one of divine origin.  An Indian is either born a Brahman or he is not.  No power on earth can make him a Brahman.  Not all Brahmans were learned even in the old days of Hinduism, though it was to their monopoly of such learning as there then was that they owed their ascendancy over the warrior kings.  Nor do all Brahmans minister in the temples.  Strangely enough the minority who do are looked down upon by their own castemen.  The majority pursue such worldly avocations, often quite humble, as are permissible for them under their caste laws.  The Brahmans were wise enough, too, to temper the fundamental rigidity of the system with sufficient elasticity to absorb the new elements with which it came into contact, and in most cases gradually to reabsorb such elements as from time to time rebelled against it.  The process by which new castes may be admitted into the pale of Hinduism, or the status of existing castes be from time to time readjusted to new conditions, has been admirably explained by Sir Alfred Lyall.  But the process can be worked