432 E. WACE CARLIER 



fore selected the white rat as the most suitable for the purpose, because it 

 is an omnivorous feeder and can be quickly bred in confinement. Unfor- 

 tunately the rat is a secretive animal, rarely eating at once the whole of the 

 food supplied to it, preferring to put aside a certain portion to be consumed 

 at leisure. I therefore set about to détermine how much food a hungry ani- 

 mal would eat at once without reserving any. After a few trials I succeeded 

 in determining to a nicety, for body weight of animal, what quantity of 

 each kind of food required in the experiment sufficed for a full meal without 

 leaving any over, by which means alone uniform results could be hoped for. 

 Ail the animais were kept under exactly similar conditions for a time and, 

 only full grown maie rats used, to eliminate, as far as possible, any fallacy 

 that might be introduced by différences of previous feeding and sexual 

 function. 



Préparation of the tissues. 



The animal was killed with coal gas, its thorax immediately opened 

 to expose the heart, the apex of which was removed and a cannula filled 

 with normal saline at the body température passed through the opening and 

 securely tied in the aorta. From this cannula, which was connected with a 

 vessel containing warm normal saline raised three feet above the level of 

 the operating table, fluid was allowed to flow through the vessels until it 

 escaped from the heart in a clear stream. The vessel was next filled with a 

 fixing solution [picrocorrosive formalin, Mann (')] warmed to body tem- 

 pérature, and about half a litre passed through the animal. This fixative 

 was selected from many that were tried, both for immersion and injection, 

 as giving the most uniform results. When the animal had become cold the 

 liver was dissected out, eut up into small pièces, placed in 50 °/ alcohol 

 and taken up the alcohol séries into chloroform and thence into paraffin in 

 the usual way. The sections were eut of uniform thickness on the rocking 

 microtome set to four teeth of the toothed wheel, fioated out on warm water, 

 mounted on albuminised slides and dried. In ail cases a controll section 

 from the liver of a fasting rat was placed on each slide and the staining so 

 carried out that the controll section was stained to exactly the same tint 

 throughout the séries. 



Various staining methods were used, most useful amongst which were 



(') For description of methods used see Mann, G. : Physiological Histology. Oxford, 1902. 



