PINEAL GLAND FUNCTION 223 



opposite phase. The salient observations that we have recorded 

 in detail on the foregoing pages are: 



1. Up to near tenth day of larval life in tadpoles, pigmenta- 

 tion is not influenced by pineal feeding. Evidences relative 

 to this are not precise, but suggest that this is due to incomplete 

 development of the nervous mechanism involved. 



2. Beginning at this time and continuing until near the ter- 

 mination of metamorphosis, the addition of traces as small as 

 1 part acetone extract in 100,000 parts water determine distinct 

 cyclic pigment changes peculiar to these preparations. Prior 

 to feeding, both controls and experimental animals are uniformly 

 dark colored. Shortly after feeding the pineal fed groups begin 

 to lose color until within thirty minutes, all macroscopic pig- 

 ment is lost so that all the larger viscera are clearly visible (figs. 

 1 and 2). The condition is transient and the cycle is complete 

 with full restoration of color within from three to six hours, 

 unless further pineal food is added to the trays. As metamor- 

 phosis is completed the pigment is no longer altered by pineal 

 materials, due to rearrangements of chromatophore types and 

 sites in the adult animal. 



3. The response in pigment change is quantitative. A method 

 is described for the standardization of pineal preparations. 



4. The pineal substance responsible for the pigment changes 

 is wholly extracted by acetone. The residue after acetone ex- 

 traction is an inert substance as to pigment influence. How- 

 ever this residue has an influence on growth and differentiation. 

 The inference is that the gland contains more than one active 

 substance. 



5. The reactions produced by pineal extracts add some evi- 

 dence to Spaeth's contention that the melanophores are modi- 

 fied smooth muscle cells. The similarity of contraction of 

 certain smooth muscle organs under the influence of pineal 

 extracts and the contraction of melanophores is in keeping with 

 Spaeth's hypothesis. 



The very nature of this pineal-pigment cycle affords an ex- 

 cellent method of approach to the mechanics of melanophore 

 function and from this the larger problems of colloidal state. 



