270 J. S. NICHOLAS 



satisfactory on the forms used by them. In some cases the 

 olfactory tracts have been cut. The latter method is the most 

 effective, but has the one disadvantage of not permitting a re- 

 turn to the normal for control experiments. The cotton-wool 

 plug has been found to have certain irritating effects upon the 

 nasal epithelium and for this reason as well as for ease of handling, 

 a collodion mask was used for occluding the nasal passages in 

 this work. 



The method is quite sunple. The animal is removed from 

 the aquarium and wrapped in a small hand towel with only the 

 head projecting. The anterior portion of the head is dried as 

 much as is possible and the collodion applied over the surface 

 prepared in this way and across the nares, making a mask the 

 shape of an inverted T, the base of the T extending well up be- 

 tween the eyes, while the cross line covers the external nares and 

 extends well around the maxilla. The mixture dries rapidly and 

 during drying causes some irritation. The animal will get rid 

 of the cap if its forefeet are free at this stage. The cap will 

 sometimes be removed by the force of the water from the mouth 

 or by an excess of mucous secretion on the front of the head, 

 but after three or four applications the animal becomes accus- 

 tomed to the mask and shows little or no sign of irritation. At 

 this stage the nose cap is more or less firmly adherent to the 

 head of the animal. The animal is replaced in the water of the 

 aquarium and generally becomes quiet in ten or fifteen minutes. 

 If the cap has remained fast during this period, it will probably 

 remain fixed for at least twelve hours, during which time experi- 

 mentation may proceed. 



The respiratory process of the animal is changed by this 

 occlusion of the nares. The animal comes to the surface and 

 'gulps' air by means of the mouth, then sinks and exhales slowly, 

 the bubbles of air escaping at the mouth. The act of respira- 

 tion affords a constant check upon the effectiveness of the nose 

 mask, for if ineffective the water current under pressure from the 

 buccal cavity will soon remove it. This mask is easily and 

 quickly removed from the animals, after which they respond to 

 control tests in exactly the same fashion as in the normal 



