498 BACTERIOLOGY. 



gathering in droplets. The turning in the air is continued till the 

 collodium layer is no longer sticky and is not too soft. It must not be 

 exposed to the air till it becomes too dry, inasmuch as it would then 

 be impossible to remove it from the glass tube. A little practice will 

 enable one to tell, by the touch of the finger, when the exposure to 

 air has been sufficient. 



"The coated end of the tube is then immersed in a beaker of dis- 

 tilled water and rotated in this for several minutes. Tne touch of a 

 finger will again indicate when the desired hardness has been obtained. 

 The tube is then withdrawn and the sac is ready to be peeled. The 

 collodium layer is cut circularly, near the upper end, and the irregu- 

 lar border is removed. With a pair of forceps or with the finger-nail 

 the edge of the collodium layer is bent back on itself. When the 

 upper portion of the collodium tube has been turned "inside out", the 

 sac can be drawn off the tube like a glove off a finger. The tube 

 is grasped over the turned portion of the sac between the thumb and 

 first two fingers. By gently drawing on this portion the sac is slowly 

 everted 



The sac thus prepared should be sufficiently firm so as not to col- 

 lapse. It is then filled with distilled water and placed in the beaker 

 of water for 15 minutes or longer. 



The next step is to prepare a glass- tube which will enable one to 

 hermetically seal the sac. The author employs for this purpose test- 

 tubes which are 2 or 3 mm. less in diameter than the sac itself. The 

 horizontal flame of the blast-lamp is directed against the test-tube at 

 a point about 4 cm. from the bottom. The tube is slowly rotated in 

 the flame and as the glass softens a constriction results. When cool 

 the rounded end of the tube must be cut off. A scratch is made with 

 a file at about 1.5 cm. below the constriction. A piece of burning 

 charcoal is then applied to the end of the scratch. By gently breath- 

 ing on the charcoal this can be kept aglow till the glass cracks. Usu- 

 ally the crack extends completely around the tube, but if it does not 

 the crack can be led around by holding the glowing coal before it. A 

 hot glass rod can be used instead of the charcoal. The cut end of the 

 tube is then heated in the flame till the border is rendered perfectly 

 smooth. The tube thus prepared has the appearance shown in Fig. 

 70 a. A number of these tubes should be prepared and kept on hand. 



When a large sac is to be used it is liable to break after it is 

 placed in the abdominal cavity. This defect is overcome by placing 

 the sac in a wide tube which is freely perforated. The following 

 modification made by the author can be employed (to advantage in 

 place of the usual method. In this procedure openings are blown into 



