The chief prison in St. Petersburg at one time was the Litovski Zamok, and it was credited with being kept clean, but the buildings, old-fashioned, dark and damp, were only fit to be levelled to the ground. A newer prison is the House of Preliminary Detention which is ambitiously designated as the “model,” and which was built on the plan of modern prisons in Belgium and at an immense cost. Kropotkin characterises it as the only clean gaol for ordinary prisoners in Russia. Cleanliness in it amounts to a craze; the scrubbing brush is never idle; broom and pail are used with demoniacal activity. Particles of asphalt dust from the floor continually load the atmosphere and make breathing difficult. The three upper stories are infected by the exhalations from the lower, and the ventilation is so abominably bad that at night when the doors are shut the interior of the cells is suffocating. Endeavours to remedy this have ended in a recommendation to rebuild the prison entirely as nothing less will serve. The cells are large enough, ten feet in length by five feet wide, and it is yet essential to keep the traps in the door constantly open to prevent asphyxiation. Strict individual separation was the rule established in this St. Petersburg House of Detention, and it extended to both cells and exercising yards. The space allotted to the latter was circular in shape and was divided into segments by walls radiating from a common centre to the circumference. Each inmate walked to and fro singly in his own compartment, under the surveillance of an official standing on a raised platform in the centre. Nothing was visible from within the partition but the backs of the lofty prison buildings topped with a narrow strip of sky. The rule of cellular isolation was defeated, however, by the ancient prison device of rapping on the walls according to a conventional alphabet based upon a fixed number of blows for each letter. The letters are arranged in certain groups as follows:— a b c d e f g h i k l m n o p r s t u v w x y z Words are composed by knocking so many times on the wall for each letter. First, the horizontal line on which the letter stands is counted and its place numbered on the vertical line. Thus to frame the word “you,” the first signal for “y” would be four knocks, indicating the vertical line; then a pause and five taps to give the place on the horizontal line. Three taps followed after a short pause by two taps would form the letter “o,” and four short taps with one final tap after a pause would fix the letter “u.” These sounds are not only distinguishable in cells alongside each other but in those far distant if the wall is the same. Communications by this means passed continually, although the system was abhorrent to the authorities and severe punishments were imposed upon all caught in the act.