136 Report of the Department of Bacteriology of the 



The drain from this cooling pipe, as shown in Fig. 1, is connected 

 with the main drain of the building through a trap. There is a 

 space of but five inches between the water level of the trap and 

 the point where the pipe leaves the incubator. This is an impor- 

 tant point; because the air within the pipe may be warmed for this 

 short distance and carry the heat into the incubator through con- 

 vection. The longer the distance, therefore, between the trap and 

 the incubator, the greater will be this warming effect upon the 

 chamber. 



It has been found in practice that when the glass tube is adjusted 

 to keep the overflow from the cooler almost as high as its entrance 

 into the chamber, and the pipe is full of water, the temperature of 

 the chamber, even without the use of a thermostat, remains fairly 

 constant at 17°-18°. If a temperature of 20° were desired, the 

 outlet from the cooling pipe could be lowered by shortening the 

 glass tube, allowing less cold water to stand inside the chamber. 

 The regularity effected by the cooler is surprising; but it is un- 

 doubtedly explained by the fact that the warmer the weather the 

 faster the ice melts and the more cold water is supplied to the cham- 

 ber. Still greater regularity is secured by the use of thermostat and 

 heater as well as the cooler, which keep the temperature constant at 

 times when the cooler alone would bring it below the desired point 



The cooler keeps the temperature of the incubator below 18 

 except when the room temperature exceeds 28°. Its failure at such 

 times might have been prevented by building a larger ice chamber 

 or possibly by constructing the cooler with more radiating surface. 

 In this climate, however, these high temperatures are so rare that 

 the arrangement described has given no serious trouble. 



The chief objection to using the drain pipe for cooling purposes 

 is its liability to clog with sediment or with the fungus growth that 

 often collects in drains of ice-chests. The sediment, however, is 

 kept out by having the overflow from the drip-pan, as already men- 

 tioned, half an inch above its floor; and the fungus growth is largely 

 prevented by putting a little copper sulphate into the pipe at inter- 

 vals. The trouble with clogging, indeed, has been very slight. 

 During the ten months of service the pipe has been cleaned out 

 but four times; and after the praccice was begun of adding the 

 copper sulphate as often as every ten days, four months passed 

 without the necessity of cleaning. The ease, moreover, with which 

 the whole cooling pipe can be disconnected makes it a moderately 

 simple matter to remove it when it does need cleaning. 



This form of cooler, indeed, has proved entirely satisfactory. 

 It is more accurate than the Panum type, and more simple than a 

 circulatory system. It also has an advantage over the ordinary 

 incubator cooled by a non-circulating stream of water in that its 

 cooling medium is especially abundant at the season when it is 

 most needed. 



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