CHAPTER 15 

 GROWTH IN TERMS OF WATER AND SOLIDS 



1. Percentage of water in the blood. 2. Refractive index of serum. 3. Per- 

 centage of water in the brain and spinal cord. 



1. Percentage of water in the blood. Hatai (MS '15) has de- 

 termined the percentage of water in the blood of a small series of 

 Norways. 



The Norways had been recently caught and were examined be- 

 fore the day's feeding. The rat was chloroformed, but before the 

 heart ceased beating it was exposed in situ, the tip clipped away 

 and the blood from it caught in a small glass weighmg bottle. 

 The fresh weight was immediately taken and after drying at 

 95°C. for a week the weight of the residue was obtained. The 

 results are given in table 208. 



2. Refractive index of blood serum in the wild Norway rat. 

 Hatai '18. The method of this determination has been given 

 on page 64. The data are presented in table 209. 



The values tend to increase with body length, here taken as 

 an index of age. The refractive index here found is slightly 

 below that for the Albino of the same body length. But when 

 thus compared the Norway is probably younger, so that if it 

 were possible to correct for age the values for the two forms might 

 come closer together. 



3. Percentage of water in the brain and spinal cord. Since the 

 percentage of water in the nervous system is most closely linked 

 with age, a precise determination in the case of the Norway rat 

 is wanting, as the age is usually unknown. However from 

 Norways born in captivity from trapped females we obtain the 

 percentages according to age, given in table 210. It is to be noted 

 that these Norways grew less rapidly than the Albinos of corre- 

 sponding age, (Donaldson and Hatai '11). This observation 

 agrees with that of King ('23). 



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