142 LABORATORY GUIDE IN PHYSIOLOGY. 



ratus. Start the siphon and note the rate of flow 

 per minute. The level of the water in the lower hot 

 tie should be probably 1 meter below that in the upper 

 bottle. Notice whether the animal seems to be respir- 

 ing normally; if so, it may be taken for granted, after 

 ten minutes, that the ventilation is sufficient. If it 

 seems insufficient one has only to increase the differ- 

 ence of level in the two siphon bottles. 



(3) Disjoin the animal cage and weigh the cage with 

 the contained animal upon the laboratory bal- 

 ances. Note the time; join the animal cage in circuit 

 again, attaching it to e, and attaching z to h. Start 

 the siphon. The greater resistance to be overcome 

 will necessitate a greater difference in the level of the 

 two bottles in order to ventilate at the same rate as 

 before. To test joints put the finger over the distal 

 tube of the Woulff bottle (a); if the joints are all right 

 the siphon stream will stop after a few moments. When 

 the water in the upper bottle is lowered nearly to the 

 end of the siphon, clamp the tube joining h to i, set 

 the empty bottle upon the floor and the full bottle 

 upon the higher level, join the tube on at k and un- 

 clamp. This whole change need only occupy a few 

 seconds. In the meantime CO 2 has been collecting, 

 but it has not been lost. 



(4) It is evident that in the afferent apparatus (a, b and 

 c) one has a means of robbing the air of CO 2 and 

 H 2 O, thus furnishing the animal with pure, dry air. 

 It is further evident that in the efferent apparatus one 

 has a means of collecting absolutely all of the CO 2 

 and H 2 O given off by the animal during the experi- 

 ment. Further the weights before and after will show 

 just how much of these excreta have been passed into 

 the collecting apparatus. 



