NERVES OF THE CONJUNCTIVA. 455 



usually met with in the interior of each bulb, which sometimes 

 form a series of coils, and in most instances originate from a 

 single afferent fibre." 



The statement of Krause, resting on these observations, to 

 the effect that the terminal bulbs constitute the only mode of 

 termination of the conjurictival nerves, was energetically dis- 

 puted by J. Arnold,* who, on the one hand, regarded the 

 terminal bulbs of Krause as not pre-existent, but as artificial 

 products, and ascribed their origin to the method of preparation 

 adopted by Krause, whilst, on the other, he described as the 

 true terminations of the nerves, a pale plexus of nerve fibres 

 situated in the more superficial layers of the tissue. Owing to his 

 mode of preparation, which consists in macerating the specimen 

 in acetic acid, or in rendering it transparent by alkalies, Krause, 

 he concluded, could not observe this plexus, since the first reagent 

 would destroy the most superficial layer of the mucous mem- 

 brane, whilst the second would render all the parts so trans- 

 parent that these pale fibres could not be perceived. The 

 terminal bulbs described by Krause might, he thought, arise 

 through the rupture of the doubly contoured fibres, partly* 

 effected in the act of preparing the specimen, but partly also 

 occasioned by the reagents applied by Krause, which lead to 

 an escape of myelin, and rolling up of the torn fibres. Both 

 circumstances would occasion the illusory appearance of the 

 internal bulb, the neurilemma of the torn fibres representing 

 the connective-tissue sheath of the terminal bulbs, and the 

 terminal fibre being represented by the axis cylinder. Every- 

 where the distal prolongation of the fibre may be discovered, 

 and it is also easy to discover ends and fragments of the nerve 

 sheath at the periphery of the so-called terminal bulbs. 



The objections raised by Arnold have found opponents in 

 Liidden and Frey, who again admit the existence of terminal 

 bulbs as a certainly established fact. Helfreich gives the 

 following details from his own researches : 



The nerves destined for the conjunctiva pass to it from the 

 inner and outer canthi, where the several branches are given 

 off from the main trunks, and pursue a more or less sinuous 



* Virchow's Archiv, Band xxvi. 



