LESSON m 

 THE BLOOD AND THE LYMPH 



1. Microscopic Examination of Blood.— In order to 

 become properly acquainted with the characters of the 

 blood it is necessary to examine it Avith a microscope 

 magnifying at least three or four hundred diameters. 

 Provided with this instrument, a hand lens, and some 

 slips of thick and thin glass,' the student will be enabled 

 to follow the present lesson. 



The most convenient mode of obtaining small quantities 

 of blood for examination is to twist a piece of string, 

 pretty tightly, round the middle of the last joint of the 

 middle, or ring finger, of the left hand. The end of the 

 finger will immediately swell a little, and become darker 

 coloured, in consequence of the obstruction to the return 

 of the blood in the veins caused by the ligature. ^A'hen 

 in this condition, if it be slightly pricked with a sharp 

 clean needle (an operation which causes hardly any pain), 

 a good-sized drop of blood will at once exude. Let it be 

 deposited on one of the slips of thick glass, and covered 

 lightly and gently with a piece of the thin glass, so as to 

 spread it out evenly into a thin layer. ■ Let a second slide 

 receive another drop, and, to keep it from drying, let it 

 be put under an inverted watch-glass or wine-glass, with 

 a bit of wet blotting-paper inside. Let a third di-op be 

 dealt with in the same way, a few granules of common 

 salt being first added to the drop. 



1 Slides and coverslips, as they are called by microscopists. 



