80 THE LUNG PLAGUE OF CATTLE. 



adduced in which a sufficient renewal of the air between decks, with or 

 without stoves to dry it, has transformed a naval pest-house into a salu- 

 brious vessel. 



All such considerations must emphasize the demand for such a con- 

 stant renewal of air between decks on steamers carrying cattle as shall 

 serve to obviate all those conditions of ill-health, with congestion and 

 inflammation of the lungs, as have proved in the past a serious draw- 

 back to our foreign cattle-trade. To accomplish this and at once re- 

 move from between decks the excess of carbonic acid, of decomposing 

 organic matter, and of humidity, and to furnish air approaching in 

 purity and dryness that of the atmosphere outside, we cau conceive of 

 nothing more simple and effective than thorough ventilation by fan or 

 heat extraction, as referred to below. 



EXPEDIENTS FOR SECURING ARTIFICIAL VENTILATION. 



Course and speed of the ship. With a wind more or less ahead or no wind 

 at all, the speed of the vessel will usually determine a current which, 

 with hatches open fore and aft, will secure a fair amount of ventilation. 

 By increasing the speed it is manifest that this may be availed of to bet- 

 ter purpose, and even a slight change in the course may often be of ma- 

 terial advantage. 



Windsails and Cowls. These are valuable if well attended to, the for- 

 mer being a sheet of canvass, so spread as to catch a greater volume of 

 air and to direct it down the fore hatch, while the cowl is a trumpet- 

 shaped tube fixed on the top of a cylindroid ventilating tube, and hav- 

 ing its open expanded end turned in the direction of the wind so as to 

 act after the manner of a windsail. These succeed well so long as the 

 weather is good and a sufficient current of air can be secured, but they 

 may prove useless in a storm or in a warm season with the wind astern 

 and moving at the same rate as the steamer. 



When they fail. In such circumstances as the last, even the usual 

 spontaneous diffusion of air may be arrested, so that the atmosphere be- 

 tween decks may remain practically unchanged for a length of time. 

 The air outside being of nearly the same temperature with that between 

 decks, there is little tendency to an upward motion from the latter or a 

 downward movement from above. Again, though there may be some 

 difference in temperature between the outer air and that between decks, 

 yet if the wind is following the ship and by reason of her pace the 

 air is practically still, the ventilation remains exceedingly imperfect. An 

 upward and downward current becoming established through the same 

 opening often neutralize each other, so that nothing more than an eddy 

 takes place near the opening, and the air within is practically un- 

 changed. In these circumstances windsails and cowls become useless 

 and some mechanical means of establishing a current must be re- 

 sorted to. 



Booby hatches. These are special ventilating hatches, constructed of 

 iron and rising four or five feet above the upper deck. They are fur- 

 nished with iron doors, or covers, sloping at a very acute angle and 

 hinged at the upper edge, so that when partly raised they serve to allow 

 the entrance or exit of air, and yet guard against the entrance of water 

 when that is shipped. These, when properly placed at the extreme 

 ends of the space to be ventilated, must be of the greatest value in 

 securing ventilation during stormy weather. But no one of the above 

 provisions meets the danger of a high temperature and a practical calm 

 aboard ship. 



