ALBINO RAT VISCERA, GLANDS, EYEBALLS: WEIGHTS 113 



For the weight of the Brain and of the Spinal Cord, formulas 

 have already been published (Donaldson '08) (Hatai '09). 



As already stated, in the case of the Tkymiis no treatment of 

 the data has yet been attempted. 



Types of graphs 



A comparison of the graphs reveals several interesting points 

 touching the form of growth characteristic for each organ. A 

 little study of the graphs makes it evident that we can class them 

 imder three general types. 



Tijpe 1. The graph represented by the growth of eyeballs. 

 This is characterized by very rapid growth in weight at an early 

 period and after this period the rate of growth is much reduced. 

 This type is characteristic for the growth of the brain and the 

 spinal cord in weight (Donaldson '08). 



Type 2. The graphs representing the growth of all the other 

 viscera except the sex glands. These graphs are characterized 

 by a relatively rapid rise at an earlier period followed by an 

 almost straight line which makes an angle of varying degree with 

 the base line; an angle always much greater than that of Type 1. 



Type 3. The graphs representing the growth of the sex glands. 

 These graphs are characterized by fluctuating rates of growth be- 

 tween birth and sexual maturity. For example, in the case of 

 the ovaries, the first phase (from birth to 50 grams) is repre- 

 sented by a logarithmic curve. This is followed by a phase of 

 rapid growth represented by a parabolic curve (50 to 110 grams). 

 This second phase is followed in turn by a phase of slower growth 

 represented again b}' a logarithmic curve. Similarly, the growth 

 of the testes has three phases, though the time relations of the 

 corresponding phases are not the same as in the case of the 

 ovaries. 



The difference between Type 1 and Type 2 is very clear when 

 the graphs are plotted to an equal scale on one sheet. When 

 this is done the graph for Type 1 appears almost parallel to the 

 base line soon after the very rapid early rise is completed, while 

 the graph of Type 2 continues to rise at a more rapid rate. When 



THE AMERICAN JOURNAL OF ANATOMl", VOL. 15, NO. 1 



