STERILIZATION. 



101 



iii all parts. It also furnishes a maximum temperature with a minimum con- 

 sumption of gas, hot air being fed to the flame. The apparatus has an inner, outer, 

 and middle wall. A horizontal iron gas pipe, of the relative size shown in the front 

 of the picture, passes entirely around the apparatus at the bottom between the outer 

 and middle wall. On top in this tube are many small openings through which 

 gas escapes and when lighted forms so many small Bunsen flames. Air is drawn 

 in at first and mixed with the gas in the middle open part of the feed 

 pipe in front. The products of combustion escape through the chimney 

 on top of the oven. There are pilot lights, so that the apparatus is set 

 going easily. The result of this arrangement is that the middle wall 

 becomes heated very hot, and consecmently the air between this w r all 

 and the inner wall rises, cool air entering through holes in the bottom 

 to take its place. There is thus created a powerful upward mount of 

 hot air. This enters the oven through several hundred holes in its 

 ceiling, is forced downward and escapes through as main- holes in the 

 floor. From this place the hot air is continually crowded sidewise and 



backward through brass tubes 

 into the furnace chamber where 

 it serves to support the com- 

 bustion. 



Unless the dry-oven has a very 

 uniform temperature through- 

 out, so that there is no danger of 

 scorching the cotton, plugged 

 test-tubes should be tied together 

 loosely and stood on end, cot- 

 ton uppermost. Petri dishes 

 (wrapped in paper as directed) 

 may be set on edge. If the 

 test-tubes have been properly 

 cleaned, dry - heating is not 

 necessary for such as are to hold 

 steam-heated media, provided 

 the cotton used for the plugs is 

 dry-sterilized in advance. The 

 best surgeon's absorbent cotton 





Fig. 86.* 



is not too good for this work. It should be unrolled and put into the dry-oven in a 

 loose armful and heated just below the scorching point for several hours (2 to 3 hours 

 at 145 C. will answer), with occasional unfoldings and turnings so that all parts 

 may be heated uniformly. It is now taken out, re-rolled and put away in clean 

 paper until needed. By this means all fungous spores lodged in it are destroyed and 



*Fic. 86. Dr. George Meyer's hypodermic syringe, made by L,auU j iiM-hl;iger. Desirable on account 

 of perfect workmanship, and because it is easily sterilized without injury. This size holds I cc. Bv 

 twisting the button of the piston the packing at the other end is tightened or loosened at will. The 

 separate parts are enlarged one-fourth. 



