134 ELEMENTARY PHYSIOLOGY. [XII. 



pletely blocked and stagnation sets in. Note 

 in the stagnated vessels the gradual oblitera- 

 tion of the outlines of the corpuscles. 



d. The emigration of the white corpuscles from 

 the capillaries and veins. This begins as 

 the circulation becomes slow; a white cor- 

 puscle which is adhering to the wall of a 

 capillary or vein should be noted at intervals 

 of 10 to 15 minutes. 



e. The diapedesis of the red corpuscles from the 

 capillaries ; this is best seen in the capillaries 

 in which the current has almost stopped. 



Notice that these effects are local, that they are 

 of greatest intensity in the spot touched, that 

 they extend for some distance round, but that 

 the circulation in the rest of the web is normal. 

 If the injury to the vessels from the creosote has 

 been slight, the circulation may be seen to be 

 re-established in the stagnated spots, the corpus- 

 cles gradually recover their outline and are carried 

 off by the current; this is not seen if stasis has 

 set in i.e. if the blood has clotted. 



7. Observe now the circulation in the tongue ; the 

 frog being on its belly, draw forward the tongue 

 over the hole in the stage and pin out the two 

 comua; the tongue at first pale soon becomes 

 flushed and its vessels full of blood. With a low 

 power the peripheral layer in the arteries and 

 veins will probably be seen better than in the 

 web. The pheiiomena of inflammation (§ 6) can 



