158 



SCIENCE 



[X. S. Vol. XXX. No. 701 



THE GRO^yTU OF NERVE FIBERS 

 The view that each nerve fiber develops as 

 an independent outgrowth from a nerve-cell, 

 finally becoming united to other tissues (e. g., 

 muscle fibers) in the periphery of the body is 

 associated especially with the name of His, 

 and has been accepted by the majority of em- 

 bryologists. Those who have worked at the 

 question of nerve repair or have studied the 

 mechanism of the regeneration of nerve fibers 

 which leads to restoration of functions are 

 divided into two camps; the majority hold, as 

 Waller originally taught, that the nerve fibers 

 grow in a distal direction from the cut stump 

 attached to the central nervous system, ulti- 

 mately finding their way into the peripheral 

 segment. A minority of researchers hold the 

 contrary view, namely, that restoration occurs 

 in the peripheral segment independently of 

 connection with the central nervous system. 



Within the last year, Mr. Ross Harrison, of 

 Yale, has demonstrated the correctness of the 

 views of His in a very remarkable way. He 

 has actually seen the fibers growing outwards 

 in embryonic structures. Pieces of the primi- 

 tive nervous tube which forms the central 

 nervous system were removed from frog em- 

 bryos and kept alive in a drop of lymph for a 

 very considerable time; the cilia of the neigh- 

 boring epidermic cells remained active for a 

 week or more; embryonic mesoblastic cells in 

 the vicinity were seen to become transformed 

 into striated muscular fibei-s, and there was 

 therefore no doubt that even under these 

 artificial conditions — rendered necessary for 

 microscopic purposes — life and growth were 

 continuing. From the primitive nervous 

 tissue, and from this alone, nerve fibers were 

 observed growing and extending into the 

 surrounding parts. Each fiber shows faint 

 fibrillation, but its most remarkable feature 

 is its enlarged end, which exhibits a con- 

 tinual change of form. This amoeboid move- 

 ment is very active, and it results in drawing 

 out and lengthening the fiber to which it is 

 attached, and the length of the fiber increases 

 at the rate of about 1 mieromillimeter per 

 minute. Those interested in this subject 

 should refer to Mr. Harrison's last paper, pub- 

 lished in the Anaiomical Record (Philadelphia, 



December, 1908), where they will find figures 

 representing the growing fibers in varioiis 

 leng-ths drawn at intervals of half an hour or 

 thereabouts. 



Such observations show beyond question 

 that the nerve fiber develops by the overfiowing 

 of protoplasm from the central cells and thus 

 give us direct ocular evidence in favor of the 

 view which most embryologists previously held 

 mainly as the result of circimistantial evi- 

 dence. It is not surprising to find that as 

 this and other facts all bearing in the same 

 direction are brought to light, the prevalent 

 idea regarding nerve regeneration after injury 

 follows the same lines. Indeed, the number 

 of those who hold the so-called " autogenetic 

 theory " of nerve regeneration is being re- 

 duced nearly to vanishing point. — Nature. 



SPECIAL ARTICLES 

 HYDROGEN POLYSULPHIDE AS A REDUCING AGENT 



When lime and " fiowers of sulphur " are 

 boiled with water and the resulting cooled, 

 clear solution poured into dilute hydrochloric 

 acid, a heavy colored liquid separates. This 

 liquid is stated by some chemists to be an 

 impure hydrogen polysulphide, whereas others 

 regard it as a mixture of several hydrogen 

 polysulphides. 



The substance has well-developed reducing 

 properties and I have found that its employ- 

 ment in organic work appears to offer consid- 

 erable advantages in many cases. 



The chief merits of hydrogen polysulphide, 

 as compared with ordinary reducing agents, 

 are as follows: It is neutral; it may be used 

 at the ordinary temperature, dissolved in ion- 

 izing solvents such as water or alcohol, or in 

 nonionizing media such as carbon bisulphide. 

 The exact quantity of hydrogen polysulphide 

 present in any of its solutions may be deter- 

 mined with great ease by titration with iodine. 



At the ordinary temperature, hydrogen poly- 

 sulphide reduces picric acid to picramic acid. 

 With nitrobenzene its reaction appears to be 

 somewhat more complicated. Further work 

 on this subject and also on the general appli- 

 cability of hydrogen polysulphide as a re- 

 ducing agent is being carried out in the chem- 



