QUANTITATIVE STUDIES ON MITOCHONDRIA IN NERVE-CELLS. 



BY MADGE DfiG. THURLOW. 



The hope of being able to establish a sound foundation for investigation 

 into cellular physiology has inspired most of the work on cell constants. Perhaps 

 the best known of these is the nucleus-cytoplasmic ratio of Hertwig (1902), which 

 has already proved of great value in the investigation of changes in nerve-cell 

 activities. On account of the reawakening of interest in mitochondria, the atten- 

 tion of investigators has been drawn in recent years to the cytoplasm. This is 

 not surprising, as structural changes resulting from experimental variations are 

 evident in the cytoplasm, for it is here that most of the products of differentiation 

 are laid down and readjustments in response to changes in the environment take 

 place. 



Though the study of mitochondria has been carried far along many different 

 lines, up to the present time no attempt has been made to place these cytoplasmic 

 structures upon a quantitative basis. With this object in view the present work 

 was undertaken, making use of a favorable method of technique. No attempt 

 was made to establish a ratio between mitochondria and cytoplasm on the basis 

 of relative volumes, the number of mitochondria per unit volume of cytoplasm 

 being the basis of comparison. This relationship has served well as an adequate 

 foundation for comparison of various nerve-cells and is thought to be of particular 

 value in the case of the nerve-cell, inasmuch as it possesses no other cytoplasmic 

 constituent lending itself to quantitative study; for the Nissl substance differs so 

 widely in form and density that it is absolutely impossible with our present 

 methods of technique to estimate its amount with any degree of accuracy, and 

 the significance and form relations of the neurofibrils are not clear. 



The original plan of the investigation was to determine whether by com- 

 parisons of the mitochondrial content of known motor and sensory cells there was 

 a distinctive difference between cells of these categories. With this purpose in 

 view, quantitative estimations of mitochondria in the nuclei of origin of the cranial 

 nerves were made. The results were disappointing, in that they showed that the 

 mitochondrial content could not be used as a basis of classification for motor and 

 sensory cells, but they did show something that was not known before, viz, that 

 the number of mitochondria per unit volume was constant for the nucleus of any 

 cranial nerve. 



MATERIAL AND METHOD. 



The animal selected was the white mouse, and the observations were confined 

 to the nuclei of the cranial nerves. The nuclei of the IX and XI nerves were not 

 included in the investigation, owing to the difficulty of ascertaining with absolute 

 certainty what cells constituted these nuclei in the nucleus ambiguus. 



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