One of the most important branches of the Post Office is the Railway Mail Service, which used to be called the Travelling Post Office. The railways are the arteries through which the very life-blood of the Department flows, and it is upon the arrangements for the conveyance of mails by rail that proper postal administration depends. Before 1863 the mail bags were carried in the guard's van if the weight was small, but when the mail was heavy a separate compartment in charge of a mail guard was used. As there was no intermediate sorting, every post office had to make up a packet or bag for every other post office in front, and these various packets were received and delivered at each station by the mail guard. In a short time the number of such packets became quite unmanageable, and the inconvenience and delay in disposing of them considerable, so that, in order to make it possible to sort the mails between North-West India and Calcutta, long detentions had to be made at Allahabad, Cawnpore and Benares, otherwise letters could not possibly be sent direct to their destinations. In 1860 a solution of the difficulty was proposed by Mr. Riddell, Director-General of the Post Office, namely, the establishment of a Travelling Post Office between Calcutta and Raneegunge, but the Government of India refused to sanction it. In 1863, however, a sorting section was established on the Great Indian Peninsula Railway between Allahabad and Cawnpore, but no regular service was organized until 1870, when the frontier Travelling Post Office was introduced under a Superintendent with his head-quarters at Allahabad. In 1877 the designation of this Officer was altered to Chief Superintendent, T.P.O., and in 1880 to Inspector-General, Railway Mail Service. The Inspector-General worked as an Assistant Director-General in the Direction until 1890, but in that year he was placed in a much more independent position as an administrative officer. Owing to the large increase in the mileage of the Railway Mail Service it was found impossible for one man to exercise an efficient control over it, and in 1905 a Deputy Inspector-General was appointed; but even with his assistance the work was too heavy, and in 1907 the whole of India was divided into four circles and each of them placed under the jurisdiction of an officer designated Inspector-General, Railway Mail Service and Sorting, known by the wits of the Department as an Inspector-General of sorts. The gentlemen with this sesquipedalian title control the railways or portions of railways in their own circles. In 1918 their number was reduced to three by the abolition of the Southern Circle, and their designation was altered to Deputy Postmaster-General, Railway Mail Service.