380 



Miss S. C. M. Sowton. Ohserxations on the 



in weight. As described by Kiihne and Steiner the E.M.F. of the 

 resting current of the olfactory nerve was found to be very high, and. 

 a few experiments, made by the " opposition method " of those authors, 

 gave results similar to theirs j that is to say, the resting current of the 

 non-medullated nerve overpowered that of a medullated nerve of 

 approximately similar thickness, whether taken from the fish itself or 

 from a frog. 



The galvanomecer used was a sensitive and quickly reacting instru- 

 ment by Siemens and Halske, of Berlin, a modified form of the 

 D'Arsonval pattern. It was used with a telescope in the usual way. 



Method. — To prepare the olfactory nerves : the head of the pike was 

 cut off, the lower jaw removed, and the head fixed to a small board. The- 

 bones of the upper surface of the skull, from the brain down to the- 

 nostrils, were removed with bone forceps, care being taken that only 

 bone was cut away, the cartilage below being left uninjured. The 

 cartilage thus exposed forms a thin capsule over the lobes of the brain, 

 becoming thicker towards the olfactory lobes, and forming, where 

 these are prolonged into the olfactory nerves, a substantial sheath 

 which encloses the nerves entirely, and through the semitransparent 

 walls of w^hich the nerves are just visible. To expose the nerves a 

 fine sharp scalpel was used, with which the upper surface of the 

 cartilaginous sheath was sliced away, great care being taken not to cut 

 too deeply and so injure the nerves themselves. Having removed in 

 this way their upper covering, the two grey nerves are found lying 

 side by side in their canal : they run parallel for the greater part of 

 their length, then fork, right and left, to enter either nostril. Before 

 attempting to remove the nerves, it must be carefully ascertained that 

 they are freely exposed in their entire length, with no overhanging 

 shreds of cartilage to catch a.nd injure them. The way being clear, 

 the end-organ of each nerve is separated from its nostril and serves as 

 a handle by which the nerve is lifted from its canal ; a clean scissor 

 cut then severs its central end from the olfactory lobe, and the nerve 

 is ready for experiment"^ (see Plate). 



The central end of the nerve was led off from transverse and longi 

 tudinal sections by brush electrodes ; their distance apart was usually 

 5 mm. The stimulating electrodes were of platinum wire, with 

 Hering'sf extra loop to cut off unipolar effects. The induction coil 

 was supplied by a single Daniell cell, the distance between primary and 

 secondary coils varying from 6 to cm. 



A good olfactory nerve, freshly prepared, gave in response to single 

 stimuli, electrical or mechanical, a negative variation that was per- 

 fectly legible on the galvanometer scale, but it must be noted that 



* If, as sometimes happened, the two nerves -were united near their central end 

 they were used together as one nerve. 



t Described by Pereles and Sachs, 'Pfliiger's Arch.,' vol. 52, p. 529. 



