338 THOMAS J. HELDT 



Finally, his method requires the preparation of the animal, its 

 anesthetization, the performance of a craniotomy or a laminec- 

 tomy, and the waiting for the effects of the anesthetic and the 

 shock of the operation to disappear. In connection with the 

 latter features, it may be well to mention that Dolley ('09 and 

 '10) has conclusively shown that the effects of the anesthetic 

 and the shock of the operation do not disappear in so short a 

 time (seven to eight hours) as Mollgaard assumes. So that for 

 various reasons, in addition to that urged by Retzius, Mollgaard's 

 technique is by no means ideal. 



It was in order to avoid the foregoing objections that the 

 technique previously described was decided upon for the present 

 investigation. The decapitation a^'oids all preliminary prepara- 

 tion of the animal, and likewise excludes the effects of an anes- 

 thetic and the prolonged shock of the operation. The apparatus 

 for the decapitation permits one to obtain practically instan- 

 taneously a segment of the animal's neck, after which the isola- 

 tion of the cord, with a little experience, requires but a few 

 seconds. By resorting to smear preparations, the freezing proc- 

 ess, which the sectioning of an unimbedded tissue demands, is 

 avoided. The smear preparations have the further advantage 

 of being fixed the very instant they are consigned to the fixative. 

 Thus it is evident that the entire procedure, namely, the taking 

 of the tissue, putting the tissue in a form suitable for study, and 

 the fixation, all occur in less than a half a minute of time, or at 

 most a minute. It should be noted that the cumbersome freez- 

 ing method of Mollgaard is designed merely to preserve the 

 tissue structure in the Sdtal condition' until thin sections can 

 be made upon which the fixative can act. The smear method 

 accomplishes this far more easily and quickly, and eliminates 

 the production of artefacts by freezing. It is of course freely 

 granted that the smear preparations do not show the minute 

 details of structure as readily as do thin sections. Nevertheless, 

 for the points in question the smear preparations are ampl}' 

 sufficient. 



In smear preparations not subjected to the freezing process 

 the Nissl's bodies and the neurofibrillae are unquestionably pres- 



