mollgaard's reticulum 337 



present in cells fixed twenty-two seconds after decapitation. 

 Small pieces of the cervical portion of the spinal cord of dog- 

 were quickly dropped in the fixative at the time stated. Then 

 in the cutting, staining, and mounting of the sections care was 

 taken to use only those sections cut from the most superficial 

 parts of the tissue block. Thus one may be reasonably sure 

 that the fixation of the superficial cells was practically simul- 

 taneous with the committal of the tissue to the fixative. 



No observations were made on imbedded specimens of frozen 



tissue. 



DISCUSSION 



It was one of Mollgaard's primary objects to produce a method 

 which would be simpler than our present neurocytological meth- 

 ods. His procedure however is not so strikingly simple as he 

 would have us believe. In the first place, the production of a 

 temperature as low as — 40°C. and the necessity for maintaining 

 it for a definite length of time requires a painstaking and rather 

 cumbersome technique. Sectioning the tissue at a temperature 

 of —20° to — 15°C. at best, and that with a specially constructed 

 microtome, is not easy. Even in the fixation, if the author has 

 correctly interpreted Mollgaard's following statement, compli- 

 cating factors enter: ''Die Fliissigkeit, in der man zu schneiden 

 wiinscht, wird in den innersten Kasten des Kalorimeters gegossen 

 und durch Zusatz von fester CO2 auf eine Temperatur von —20° 

 bis —25° heruntergebracht." Judging from the description of 

 his apparatus this seems an unnecessary step, yet he so directs 

 us. Bohr (Annalen der Physik, IV F, Bd 1, S. 244, 1900) states 

 that at -20° and -40°C. (760 mm.?) 98.7 per cent (by weight, 

 15°, 760 mm.) ethyl alcohol will absorb 7.16 cc. and 13.89 cc, 

 respectively, of COo (0°, 760 mm.). In 96 per cent (the per- 

 centage used by Mollgaard) alcohol the absorption is of course 

 less. However, Mollgaard thus leaves without control the possible 

 changes the tissue may suffer from the effects of the COo. At 

 the temperature stated it may be questioned if there is any 

 effect on the tissue, still it cannot be nil. The presence, and its 

 liberation as the temperature rises, of the CO2 in the fixative 

 does not simplify the technique to say the least. 



