CH. VIIl] FROGS, TOADS, AND NEWTS 255 



juice are poured simultaneously upon the food almost 

 immediately after it issues from the stomach. By these 

 two fluids the digestion of the proteids, carbohydrates and 

 fats of the food are completed. The green colouring matter 

 of the bile is, in part at any rate, a derivative from the 

 haemoglobin, or red colouring matter of the blood. Glycogen 

 is stored up in the hepatic cells as the result of digestion 

 and absorption in the intestine : the absorbed food is 

 conveyed to the liver by the portal vein and there converted 

 into glycogen, pending the demands of the general tissues 

 of the body. As occasion arises it is converted into more 

 soluble material, a sugar, and sent into the main blood- 

 stream via the hepatic veins and inferior vena cava. Fat 

 globules are also contained by the liver cells. The storage 

 function of the liver is one of considerable importance, 

 especially during hibernation and at the breeding season ; 

 the weight of the organ exhibits a well-marked seasonal 

 variation in accordance with the amount of reserve food 

 contained. The details of this phenomenon have been 

 worked out by Alice Gaule 1 in Rana esculenta. The 

 breeding season of this frog is in May, June, and July. 

 The table on the next page shews the average weight of 

 the liver in the two sexes month by month. 



It will be observed that the liver is most depleted in 

 both sexes in June, the middle of the breeding season, and 

 that it reaches its maximum weight in September when 

 the system has recovered from the exhaustion of spawning. 

 Throughout the winter the reserves are being steadily 

 used up, with no recovery by the female, the average 



1 Pflilger's Archiv f. ges. Physiol. LXXXIV. 



