236 



Mr. J. N. Langley. Variations of [Nov. 19, 



Effect of Digestion. — When frogs are fed, e.g. y with worms, the fat 

 in the liver at first decreases, after some hours it begins to increase 

 and becomes greater than at the beginning of digestion ; towards the 

 end of digestion it decreases again in amount, so that in one or two 

 days the amount is normal. Whilst the fat is decreasing in amount, 

 the globules usually decrease in size ; whilst the fat is increasing in 

 amount, the globules usually increase- in size, and are found in the 

 outer region of the cells.. Later, as the fat returns to normal, the 

 globules form more and more an inner zone. 



The extent of the changes just mentioned as occurring during 

 digestion, as well as the period of digestion at which they occur, 

 varies very considerably at different times of the year, and in different 

 frogs. Winter-frogs which have before digestion much fat in the liver, 

 show a decrease and subsequent increase of fat during digestion, but 

 the increase is commonly not more than sufficient to bring the fat 

 up to the amount present before food was given. 



In some cases in summer-frogs, especially in September and Octo- 

 ber, the effect of feeding is very slight. There are also- certain 

 differences in the distribution of the fat- globules in different frogs, in 

 the several stages of digestion. Usually when there are many fat- 

 globules present in the outer part of the cells before digestion, they 

 increase in number during the first stage of digestion in the inner 

 part of the cells ; but this is not always the case, whilst disappearing 

 from all parts of the cell, they may disappear much more rapidly from 

 the inner than from the outer cell-region.. 



Further, when fat-globules are present in the inner zone only, it 

 may happen that, although they increase somewhat in number in the 

 cells in the later stages of digestion, they do not accumulate in the 

 outer cell-region, but are sparsely scattered in the outer cell-region, 

 and are more numerous in the inner cell-region. 



Probably. these differences are to be accounted for in the following 

 way. 



We have seen that when fat is present in considerable amount, 

 it is present almost without exception in greater quantity in the outer 

 than in the inner part of the cells, and that in most cases, as it is 

 increasing in amount, whether from decrease of temperature, or from 

 digestion, it increases in the outer part of the cells, frequently being 

 found close to the basement membrane. Hence we may conclude, 

 that fat is formed more rapidly in the outer than in the inner part of 

 the liver- cells. 



We have seen that when winter frogs are kept in the warm, it is in 

 the outer portion of the cells that the fat chiefly disappears, and that 

 in summer-frogs, fat is rarely found except in the inner cell-region. 

 Hence probably the metabolism as well as the formation of fat is more 

 rapid in the outer than in the inner cell-region. 



