Reprinted from THE JOURNAL OF BIOLOGICAL CHEMISTRY, VOL. XIV, No. 3, 1913 



CONTRIBUTIONS TO THE CHEMICAL DIFFERENTIA- 

 TION OF THE CENTRAL NERVOUS SYSTEM.. 



II. A COMPARISON OF TWO METHODS OF PRESERVING NERVE 

 TISSUE FOR SUBSEQUENT CHEMICAL EXAMINATION. 



BY W. KOCH AND M. L. KOCH. 



(From the Hull Laboratories of Biochemistry and Pharmacology, University 

 of Chicago, and the Wistar Institute of Anatomy, Philadelphia.) 



(Received for publication, February 20, 1913.) 



With valuable biological material it is sometimes desirable to 

 make water estimations and the estimations of the other constitu- 

 ents on the same sample. This can be done somewhat indirectly 

 if the method already described 1 of placing the fresh, weighed 

 tissues immediately in 95 per cent alcohol is used. 



To see whether tissues in which the water had been determined 

 by drying could thereafter be analyzed by the methods referred 

 to above and would yield the same proportion of the various con- 

 stituents as these same tissues treated by the alcohol method, an 

 analysis was made of the brains and spinal cords of albino rats 

 which had been dehydrated in these two ways. The possible 

 drawbacks of the heat method of determining moisture, namely, the 

 oxidation or decomposition of part of the material and the evapora- 

 tion of volatile constituents, are obvious, but we had no definite 

 knowledge of how serious the errors involved in the method might 

 be in practice. 



To determine to what extent these changes took place and what 

 they were, we analyzed material which had been dried at 95C. 

 for one week and which at the end of this time had been placed in 

 alcohol, and compared it with similar material which had been 

 placed directly in alcohol. The results are given in the table. 



It may be seen by a comparison of the results of the two analyses 

 in the table, that decompositions seriously affecting the analyses 

 are produced by heat drying, particularly in the case of the brain. 

 The differences are most marked in the phosphorus compounds. 



1 Koch, W. : Journ. Amer. Chem. Soc., xxxi, pp. 1353-4, 1909. 



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