550         NIOHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE
Net Register Tonnage is the residual tonnage after various
allowances for propelling power, crew spaces and navigation spaces
have been deducted from the gross tonnage.
Canal dues are payable on the tonnage stated in the certificates
granted by the Panama and Suez Canal Authorities respectively.
The assessable tonnage space is based on the Panama and Suez
rules which, in some respects, differ from each other and from
the British rules, so that all vessels using these Canals must be
inspected and measured for these certificates. The Panama Canal
net tonnage is based on the ship's actual earning or cargo carrying
capacity, and includes all covered in spaces such as forecastle,
poop, bridge space, shelter deck or 'tween decks, and this tonnage
determines the canal dues to be paid by the ship. The tolls are
$1.25 per ton for loaded vessels and $0 75 per ton when in ballast
with, in the latter case, a restriction as to the quantity of bunkers
that may be allowed in lieu of ballast. The Suez Canal toll is 5/9 per
ton for loaded ships and half that amount for vessels in ballast, with a
levy for passengers: 5/9 for each adult and 2/10J for each child
between 3 and 12 years of age. Additional charges are made by
both Canal Authorities for pilotage, towage, etc.
MINISTRY   OF   HEALTH.
Port Local Authority.—When a vessel enters a port from
overseas she is visited by the boarding Medical Officer of Health,
to whom the master gives in the following form a " Declaration of
Health." If the ship is healthy the medical officer certifies that he
has examined the ship and finds no medical reasons for withholding
pratique.
The Immigration Officer ascertains, with regard to aliens
entering the country, the length of their stay, the purpose of their
visit and the amount of money in their possession. No alien is
allowed to land who is a lunatic or mentally defective, or suffering
from T.B., leprosy, etc., or in a verminous condition.
DECLARATION   OF  HEALTH
(To be rendered by the Master of a foreign-going ship arriving in Great Britain
or Northern Ireland from a foreign port)
the attention or the masteb is DniECTED to the instbuotions
xinpeb articles 5, 6 and 19*
Name of Vessel	,..„	„	
From	        Via	
Nationality	        Net Registered Tonnage