154 THE BIOLOGY OF THE FROG CHAP. 



The liver of the frog generally contains a considerable 

 amount of pigment. Two forms of pigment occur, accord- 

 ing to Leonard, the black or dark brown, and the golden. 

 A certain amount of pigment granules occurs in the ordinary 

 cells of the liver parenchyma, but most of this substance is 

 found in pigment cells which are scattered about through 

 the whole organ. 



Eberth held that the pigment cells lie within the blood 

 vessels, and that they resulted, in large part at least, from 

 the transformation of leucocytes. Ponfick and Leonard 

 regard them as lying outside the blood vessels in the peri- 

 vascular lymph sinuses. Braus, however, finds pigmented 

 cells both in the blood and in the lymph vessels. 



There is no evidence that the pigment cells are derived 

 from the ordinary secreting cells of the liver (Oppel). 

 Colorless amoeboid cells have been observed in the lymph 

 spaces of the liver, and it is not improbable that a large part 

 of the pigment cells may result from the accumulation of 

 pigment by such cells which have wandered into the liver 

 from other sources. 



The secreting cells of the liver present different appear- 

 ances in relation to changes in their activity. The granules 

 of the cells were found by Langley to increase in number 

 after a meal. " The changes are much more marked when 

 the cells have, to start with, a small outer non-granular zone ; 

 in such cases in the 6th to 8th hour of digestion, the outer 

 zone is large, and in the 24th to 3oth, the cells become 

 granular throughout." The decrease of granules was found, 

 as a rule, to be accompanied by an increase in the glycogen 

 in the cells, and vice versa. From analogy with the behavior 

 of similar granules in other gland cells, Langley considers 

 the granules in the liver to be concerned in the secretion of 

 bile. Lahousse finds that granules disappear from the cell 



