THE NEURO-MUSCULAR SPINDLE 123 



which makes it impossible to distend the tissues sufficiently. 

 In these I use one of the placental vessels, ligating all the others 

 so as to direct the solution into the embryo. For the smallest 

 sizes I had to use an hypodermic needle instead of the glass 

 cannula. When enough of the solution is injected, all the um- 

 bilical vessels are clamped off with a small hemostat. Then the 

 embryo is placed in the thermostat for five to ten minutes, vary- 

 ing according to the size of the specimen. For the dissection 

 of the eyes it is necessary to use instruments which have been 

 kept in normal salt solution. In removing the eyes, dissect away 

 the skull bones and cartilages, brain and sphenoid bone, so as to 

 keep all the muscles attached to the eyeball. Then fasten the 

 eye down to paraffin at the bottom of a pan with enough salt 

 solution to cover the eye. The muscles are carefully removed and 

 examined in salt solution on a clean slide. This allows the dye, 

 which has become reduced and thus colorless in its union with 

 the nerves, to oxidize and become blue. If the endings do not 

 appear at once, place the muscle in the thermostat and examine 

 it every few minutes. I found that it never took more than ten 

 minutes for the endings to appear. The study was confined 

 entirely to the extrinsic eye-muscles — except the checking of the 

 results on the limb muscles — for several reasons. Many of the 

 related problems had been thoroughly worked out upon the eye- 

 muscle in pigs, such as their development, the time of connec- 

 tion with the cranial nerves and the structure of the adult sensor}^ 

 endings. Besides these, there is this advantage; in the earlier 

 stages the muscles are so small that one can examine the entire 

 muscle in a single preparation. 



As soon as the nerves appear the tissue is ready to be fixed. 

 There are two ways of fixation. One is to place the tissue in a 

 large amount of 8 per cent ammonium molybdate (Merck or 

 Kahlbaum) overnight in an ice-chest. This entire method is 

 best carried out with the reagents kept on ice. Then wash the 

 tissue in ice-water one-half to two hours. Remove it from the 

 water and pass it through several changes of 96 per cent alcohol 

 at a low temperature for one-half to two hours, then through 

 several changes of absolute alcohol for one-half hour. It can 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 18, NO. 1 



