CORRELATIONS AND VARIABILITY OF THE CENTRAL 



NERVOUS SYSTEM AND BODY SIZE 



OF THE ALBINO RAT. 



FREDERICK S. HAMMETT, 

 THE WISTAR INSTITUTE OF ANATOMY AND BIOLOGY, PHILADELPHIA. 



A knowledge of inter-organ weight relationships gives data 

 which assist in the making possible a more exact conception of 

 differential development. The presence or absence of a statistical 

 association may indicate the presence or absence of a community 

 of growth response to general developmental factors; it may 

 indicate the presence or absence of a specific conditioning of the 

 one organ by the other; or it may indicate the play of reciprocal 

 influence. 



The use of the coefficient of correlation in an investigation of 

 this problem is marked by its neglect. What little the literature 

 does contain, is, with one or two exceptions, sketchy and in- 

 adequate. It is usually a mere record of figures which in many 

 cases are of meagre value because of the paucity of raw data. 



Realizing the need for a more systematic survey of inter-organ 

 weight relations a beginning was made somewhat over a year ago 

 with a biometrical analysis of the weight interrelations of the 

 glands of internal secretion. A preliminary note was published 

 in Endocrinology (i) in anticipation of full presentation in the 

 Journal of Metabolic Research at some future date. In the latter 

 there will be found the conditions which should govern a study of 

 this nature. The present paper is an extension of the analysis 

 to the brain and spinal cord, using as raw data the body weights, 

 body lengths, brain weights and spinal cord weights of, the same 

 rats the organ weights of which served for the earlier study. 

 These animals were the controls of the studies of the thyroid 

 apparatus (2). They were 150 days of age at the time the organs 

 were removed for weighing. Both sexes were used, 121 rats of 

 each. They all came from the Experimental Colony Stock of 

 The Wistar Institute. The values thus represent the associations 

 found in the mature male and female albino rat of this stock. 



509 



