Historically it may be gleaned from the fragmentary references which we have given, that soured milk has, from time immemorial, formed the principal article of diet of a great many peoples, and the notable feature in connection with it is, that in some countries where it is in daily use, the age limit for human beings seems to be very much extended, and it would appear that there is a direct connection between the use of soured milk and longevity. In Bulgaria, for example, it is stated that the majority of the natives live to an age considerably in excess of what is recognised as the term of life amongst Western nations, and inquiry has shown that in the eastern part of Southern Europe, amongst a population of about three millions, there were more than three thousand centenarians found performing duties which would not be assigned to a man of sixty-five years of age elsewhere. It is quite common to find amongst the peasants who live to such a large extent upon soured milk, individuals of 110 and 120 years of age.[13] In the ancient dairy practice, as we have seen, soured milk was the principal product, and the extraordinary ages which are recorded of the patriarchs, if translated into the modern denomination, would not appear to be so imaginary after all, when it is considered that we have thousands of examples at the present day of men and women enjoying quite as long a term of existence. It has been noticed also, that while these very old people are able to perform a certain amount of manual labour, there is not the same tendency to the mental decay which is so prominent and sad a feature amongst Western nations, at a period of about seventy or eighty years of age. It would seem, indeed, as if the habit of living long was well known in ancient times, and that, like many other of the valuable arts and sciences, it fell under a cloud during the Middle Ages, or, perhaps, the significance of the use of soured milk fell into neglect, and, even after the revival of letters in the sixteenth century, still remained obscure.