SACK'S RULE 



367 



TABLE LXXI1. 



Table LXXII. is from Pfaundler's data. It gives the calculated 

 and observed weights for each age as well as his values for m and 

 the centimetre index. 



The ratio, weight in Kg. /length in cm., is called the centimetre index. 

 Sometimes the ratio is modified as in Levi's ratio, which is 



100 f/wt. in grams 

 length in cm. 



This ratio diminishes as age increases up to puberty. 

 Dreyer suggests that instead of the total length of the body it would be 

 better to deal with the sitting height. 

 He has established the following ratios : 



Males, W= 0-38025 ' 3 ^/l; 



Females, W = 0-36093 ' 31 f/l ; 



where W = weight of the body in grams 



and I length of trunk in cm. 



Some organisms when their size reaches a certain limiting 

 value tend to divide into two equal portions (Sach's Rule). There- 

 fore, one has to deal with an increase in number quite apart from 

 increase in individual size or weight. It has been proved by 

 numerous experiments that the increase in the number of cells 

 follows the compound interest law, i.e. is an autocatalytic reaction. 



To summarise : When it is said that growth is an autocatalytic 

 reaction it is inferred that (i) superimposed on the velocity of 



