eanvier's constrictions in the spinal cord. 95 



nuclei sometimes lie against the myelin, but I have found no 

 proof that these do not belong to the neuroglia. The myelin 

 was not broken by the incisures of Schmidt and Lantermann. 



The value of these results depends of course on the value 

 of the method by which they were obtained. Well-founded 

 objections have been brought against nitrate of silver. This 

 reagent may be reduced in all parts of the nerve-fibre, and 

 even between the individual fibres.^ Combinations of various 

 forms of impregnations give a great variety of pictures. In 

 teased preparations, for reasons previously stated, the crosses 

 are not often found isolated. These facts make deception 

 easy, but do not lessen the force of the truth that unmistak- 

 able crosses are proof of the presence of Ranvier's constric- 

 tions. It may be said that the constrictions found in osmium 

 preparations were artificially produced. Naturally, the only 

 evidence which can be offered here is the testimony of accu- 

 rate drawings. 



The demonstration of the presence of constrictions in cen- 

 tral fibres helps directly in the settlement of some vexed 

 questions and is of indirect value with respect to many others. 



Ranvier- advanced the opinion in his original memoir that 

 the myelin is impervious to crystalloids, and that nitrate of 

 silver enters the nerve at the constriction. This, he said, goes 

 to show that nutritive fluids take the same route ; and his 

 explanation is accepted by most physiologists. There is, as 

 Boveri insisted, no reason for supposing that the nutrition of 

 medullated central fibres is different from that of medullated 

 peripheral fibres. Boveri,^ not finding the constrictions in 

 the spinal cord, rejected Ranvier's hypothesis and substituted 

 his own, which was that the constrictions served a purely 

 mechanical end, permitting great freedom of motion, like a 



1 I can confirm KoUiker's statement that stripings similar to Frommann's 

 lines occur in silver preparations of small blood-vessels. Boll (I.e., p. 310) 

 saw cross-striping in elastic fibres treated with nitrate of silver. 



^ " llecherches sur I'Histologie et la Physiologic des Nerfs,' ' Arch, de 

 Physiologic,' iv, Mars, 1S72, No. 2. 



' " Beitrage zur Kenntuissder Nervenfasern," 'Abhandl. der miith. phjsik. 

 classe d. k. Bayer. Akad. der Wissensch.,' Bd. xv, 1886. 



