344 THOMAS J. HELDT 



the Nissl's bodies as composed of substances of the nature of 

 chromatin, as is generally done, then we may say that the blue- 

 staining (with toluidin-blue) networks or reticula are derived 

 from the Nissl's bodies and nuclear chromatin of the nerve cells 

 as well as the nuclear chromatin of all other cells present in the 

 preparation. The pink-staining (with erythrosin) networks, on 

 the hand, may be regarded as arising from all the achromatic 

 substances of cellular cytoplasm and tissue (blood, lymph, etc.) 

 alike. That such is indeed the origin of the networks or reticula 

 is confirmed by this investigation. Mollgaard's reticulum there- 

 fore arises from the Nissl's bodies and nuclear chromatin. The 

 reticulum is a product of the Nissl's bodies rather than the 

 converse as believed by Mollgaard. The close relationship 

 between the reticulum and the Nissl's bodies is further supported 

 by the many transition forms that may be noted in nerve cells 

 of smears frozen at moderately low temperatures ( — 5° to — 25°C.) 

 (figs. 3 and 4). 



Retzius in his study of the freezing of various tissues and fluid 

 masses lays much stress on the foraiation of a system of clefts 

 and lacunae due he says to the collection of the water at the 

 moment of freezing at the points of lowest resistance. The for- 

 mation of ice in this system produces distortion and laceration. 

 With fixation the entire picture is preserved and is known to 

 us as the artefacts due to freezing. Excepting for the undue 

 stress laid on the formation of a system of clefts and lacunae 

 and the production of real laceration, it is evident that Retzius' 

 results are in the main quite similar to those arrived at in this 

 investigation. The cleft and lacunar system of Retzius, how- 

 ever, must not be confused with the clefts spoken of here as due 

 to the contraction of the ice present. 



CONCLUSIONS 



From the observations presented and the discussion made the 

 following conclusions may be summarized: 



1. With a simplified smear method, both the Nissl's bodies 

 and the neurofibrillae are found present in the spinal nerve 

 cells of the dog, fixed twenty-jive seconds after decapitation. 



