332 William E. Kellicott 



These curves of relative weight are again all of the same general 

 type though individually distinct. The heart, pancreas and spleen 

 (Plates 2, 4, 5) are essentially alike in showing first a rapid increase 

 in relative weight followed by a somewhat less rapid fall and then a long 

 and slow but steady decline through to the end of the series. Indi- 

 vidually these differ in the extent of the initial rise, in the rate and 

 duration of the first and second phases of decline and in the total amount 

 of decline. In the brain and rectal gland (Plates 1, 3) the initial phase 

 of rapid rise is omitted, the entire curve resembling in general the de- 

 clining parts of the preceding curves. Of all the curves, that of the 

 rectal gland shows the most nearly horizontal line in its latter part. 

 The first parts of the curves given by the liver and gonads (Plates 6, 7) 

 are similar to those first mentioned in showing the initial rapid rise and 

 similarly this is followed by a considerable decline. This decline, how- 

 ever, is checked and the curves soon become somewhat irregular, the 

 testes showing a very pronounced rise, the ovary and liver considerably 

 less. 



It is hardly necessary to point out that the relation between these 

 curves and the base line of body weights expresses the relation between 

 the relative rates of growth of the particular organ and the entire body. 

 Should these lines be parallel the two are growing at relatively equal 

 rates; when the curve rises or falls the particular organ is growing 

 respectively faster or slower than the body as a whole. The growth 

 of an organ by the addition of constantly equal increments, as described 

 above, would give a curve or line, depending upon the actual size of the 

 increment, tending to approach the base line, which simply expresses 

 the fact that equal increments added become smaller relatively as the 

 organ and the body increase in size. With certain initial size relations 

 among organ, increment and total weight, addition of constantly equal 

 increments would give a curve showing first a rapid rise and then a 

 slower and long continued fall, much as we find in some of these curves, 

 for example, in the heart, which increases regularly at the rate of 0.85 

 gram per 1000 grams total weight. Should the added increments con- 

 stantly decrease in amount the curve would approach the base line more 

 rapidh% or should the increments increase the curve might become par- 

 allel with the base as in the rectal gland, or it might even rise as in the 

 testes. 



In discussing the possible significance of these curves it is convenient 

 to consider the liver and gonads separately later. It is evident that 



