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



CONTRIBUTIONS TO THE CHEMICAL DIFFERENTIA- 

 TION OF THE CENTRAL NERVOUS SYSTEM. 



I. A COMPARISON OF THE BRAIN OF THE ALBINO RAT AT BIRTH 

 WITH THAT OF THE FETAL PIG. 



BY MATHILDE L. KOCH. 



(From the Hull Laboratory of Biochemistry and Pharmacology, University of 

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



(Received for publication, February 20, 1913.) 

 INTRODUCTION. 



For the study of the progressive changes in the central nervous 

 system during growth and senescence, the albino rat, on account 

 of its small size, short span of life and its powers of rapid reproduc- 

 tion 1 is especially suited. Its growth processes are, moreover, 

 strikingly like those of man, as has been brought out by the exten- 

 sive investigations of Dr. Donaldson within the past few years. 

 It was, therefore, decided to use this animal for a study of the 

 chemical differentiation of the central nervous system during 

 growth. 



The youngest brains which could be conveniently collected for 

 chemical analysis were those of rats just born. As it was not 

 certain that the rat at this period of development was sufficiently 

 immature (chemically undifferentiated) to serve as the starting 

 point for such a growth series, it was suggested by my brother, 

 Dr. Waldemar Koch, that the brain of the new born rat be com- 

 pared chemically with the brain of the fetal pig, collected at vari- 

 ous stages of fetal life. 



By such a comparison we hoped to determine the physiological 

 age of the rat at birth in terms of fetal pig material; and to obtain, 

 possibly, from the pig fetus, material which would be more imma- 

 ture than the new born rat. 



1 H. H. Donaldson: President's Address, Journ. of Nervous and Mental 

 Disease, xxxviii, p. 258, 1911. 



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