NOTE ON THE FOKMULAS USED FOE CALCULATING 

 THE WEIGHT OF THE BRAIN IN THE 

 ALBINO RATS. 



BY 



SHINKISHI HATAI. 



Associate in Xciiyolofju at The Wistar Institute. 



In previous papers (Hatai, '08; Donaldson, '08) the formnlas for 

 calculating the weight of the brain and of the spinal cord in rela- 

 tion to the body weight were determined on the assumption that 

 the amount of increment to the weight of these parts is proportional 

 to the reciprocal of the body weight plus a constant or 



^=h— ^ (1) 



a^ (x + a) ^ ^ 



where y is the weight of the brain or spinal cord in grams and 

 X the weight of the body in grams. 



Integration of (1) gives at once the value of y. 



Thus : 



y=h f (x + a) ^^"^^ ^"^ ^^ + a) + c 



(X + a) 

 or in our previous notation (Donaldson, '08) : 



y = A + C log (X + ;^) (2) 



This type of logarithmic formula has been used by the present 

 writer ('08) and Donaldson ('08) and was found to be very sat- 

 isfactory for representing the relation between the body weight and 

 the weight of the brain or spinal cord. 



This type was further employed by Donaldson ('09) to repre- 

 sent the relation between the body weight and body length and was 

 proved by him to be satisfactory. 



The .ToiRXAL of CoMr-vnATivE NEfnoLouv and rsYciior.dOY. — Vol. XIX, No. 2. 



