CIRCULATION OF THE BLOOD. 



In the smaller and narrower vessels where only one corpuscle at 

 a time can get through, note the adaptability of the red cells, 

 through their elasticity, to the varying calibre of the vessel. 



3. The Migration of the Leucocytes. Dip the point of a 

 pin into strong acetic acid. Touch the web with the acidulated pin 

 point. Note the ensuing effect upon the circulation through the 

 web as a whole and particularly upon that part in the immediate 

 vicinity of the irritant. 



Examine a small vessel with the high power. How does the rela- 

 tive number of reds and whites compare with the relative number 

 in the non-irritated web ? 



Find a portion of the web free from pigment, where a capillary 

 may be seen whose walls are distinctly visible. Pick out some leu- 

 cocyte lying against the wall of the vessel and observe it closely. 

 If a good field has been selected, the corpuscle will be seen to make 

 its way, gradually, through the capillary wall. Make a series 

 of sketches showing the progress of the corpuscle through the wall 

 until it is entirely outside of the vessel. After a time many white 

 cells will be found outside of the vessels in the surrounding tissue. 

 This process is known as the migration of the leucocytes and oc- 

 curs in other inflammatory conditions where the specific irritant is 

 some micro-organism or bacterial toxin. 



Where the~resulting inflammation is more severe, the vessel walls 

 may so change as to allow the passage of the red cells as well as that 

 of the whites. The white cells, however, pass through the vessel 

 wall by means of their amoeboid movement, while the reds, in their 

 passage, are entirely passive, being forced through by the pressure 

 of the blood in the vessel. 



4. Repeat the observation of the capillary circulation, using the 

 frog's mesentery instead of the web of the foot. 



The mesentery is so sensitive that simple exposure to the air acts 

 as a sufficient irritant to cause an exhibition of all the phenomena 

 of inflammation. 



Make a drawing of the capillary circulation as seen in the mes- 

 entery and in the web of the frog's foot. 

 6 [Si]. 



