342 ELECTRO-PHYSIOLOGY CHAP. 



medullated nerve-fibre, " bearing only a single end-disc." In other 

 cases the twig runs on without branching, and bears two, three, 

 or more end-discs, which may be of a considerable size. Every 

 possible transition exists between these simple forms and the 

 most complicated ramifications of the axis-cylinder. But what- 

 ever the mode of ending of the motor nerve-fibres, there is never 

 with either gold method or methylene blue an " intravaginal 

 nervous reticulum " in Gerlach's sense (53); the contact between 

 nerve- and muscle-substance is always distinct and confined to the 

 immediate vicinity of the point of entrance. It is obvious that 

 this point is of crucial importance to physiological theory, for our 

 views of the relations between nerve and muscle would have to 

 be considerably modified if it were true, as Gerlach says, " that 

 the presence of nervous elements is implied wherever there is con- 

 tractile substance, and that no sharp separation between nervous 

 and muscular tissue can be accepted." Long before any good 

 results had been obtained with vertebrate muscle (where, owing 

 to erroneous interpretation of gold preparations, Gerlach's con- 

 ceptions had been accepted), valuable work was done by means 

 of methylene blue, with the muscles of certain arthropods. 



In the crayfish it is easy to stain the nerves of the trunk- and 

 tail-muscles so clearly that no doubt can exist as to the finest 

 endings of the rami of the axis -cylinder. Under such condi- 

 tions, both the wide band-shaped muscles which run along the 

 ventral surface of the thorax, and the superficial layers of the 

 muscles of the tail, exhibit an extraordinary wealth of nerves. 

 The smallest particle from the surface of a nerve thus stained is 

 seen under the microscope to be interwoven, and studded with 

 a more or less dense tissue of the finest axis-cylinders, stained 

 blue, and characterised by richly varicose swellings. These arise 

 from the branching of the larger trunks (containing several axis- 

 cylinders of unequal size, and depth of stain), which traverse the 

 muscle throughout its volume. Ehrlich, who was first to observe 

 the effect, is of opinion that this really is an " intramuscular 

 plexus " (corresponding with Gerlach's " intravaginal nervous reti- 

 culum "), and that there is a fundamental distinction between the 

 mode of nerve-ending in these muscles and in those of the ex- 

 tremities, where (in his words) " the nerves run an isolated course 

 and form superficial ramifications, which rarely stain with methy- 

 lene blue." 



