52O FREDERICK S. HAMMETT. 



variable tissue. The one is, by virtue of its chemical make-up, a 

 relatively fixed structure, the other a fluctuating mass freely 

 subject to many influences. 



The fact that the body length variability of the rat is of the 

 same order of magnitude as that of man is indicative of a bio- 

 logical similarity in inherent structural response to factors con- 

 tributive to variability, which might well have been predicted 

 from the very nature of the structures involved, and which is 

 support for the idea expressed in a preceding paragraph that the 

 species difference in body weight variability exhibited here is 

 factored in part by difference in racial uniformity of population 

 from which the data were derived. 



The lesser variability of the body length combined with the 

 fact that the variability in brain weight and spinal cord weight is 

 closer in degree to that of body length than to that of body weight 

 establishes the conclusion postulated by Donaldson (5) that body 

 length is a better datum from which to infer brain and spinal cord 

 weight, than is body w r eight. 



Both brain and spinal cord are less variable than the body in 

 weight. This also holds for man in the case of the brain. Pearl 

 (u) records a C.V. value of 7.5 to 8.8 for the male brain, and 7.1 

 to 8.7 for the female, while Blakeman (10) found 7.8 for the male 

 and 8.2 for the female. 



The lower variability of the central nervous system is obviously 

 again an expression of an inherently more stable chemical make- 

 up. Evidence for this is had both in the fact that the brain and 

 spinal cord are more resistant to conditions of malnutrition and 

 inanition than is the body as a whole (15), and in the fact that the 

 growth of these organs is more resistant to the metabolic upsets 

 incident to thyroid and parathyroid deficiencies than is that of 

 the body in weight (16). This has been discussed in another 

 paper. All that need be pointed out here is that the high content 

 of the central nervous system in characteristically stable lipoids 

 determines in it a resistance to metabolic disturbances which 

 primarily affect the more readily utilizable tissue components, 

 such as occurs in inanition, thyroid deficiency and individual 

 dietary idiosyncrasies affecting body weight. 



A- >ne after another point of view is used in the attack on the 



