III.] HtJMAN BLOOD. * I < 



Bi/ii:;ed, e.g., by picro-cannine, and keep well when mounted in glycerine 

 jelly. 



33. Leucocytes of Crayfish Blood or Haemolymph. The colourless blood of 

 the crayfish does very well for the study of colourless corpuscles. Make a slit 

 in the ventral surface of the abdomen between the rinjrs and the blood flows 

 freely. Receive it in normal saline solution. It clots quickly. Mount some on 

 a slide, and if it be desired to fix the corpuscles, allow a jet of steam to play on 

 the cover-glass for a few seconds. If the fluid contain too much blood there is 

 so much coagulable proteid, that on its coagulation by the steam a white film 

 obscuring the leucocytes is formed. The corpuscles can be subsequently stained 

 with picro-carmine and mounted in glycerine. The blood contains two forms 

 of corpuscles one with well-marked amoeboid movements and provided with a 

 large spherical nucleus ; the other filled with highly refractile granules, which 

 stain red with picro-carmine. 



The best method is to allow a drop of blood to fall into a large drop of I 

 per cent, osmic acid previously placed on a slide. This at once kills and 

 " fixes " the corpuscles, which can then be stained with picro-carnaine, or I per 

 cent, watery solution of eosin. The latter stains their protoplasma and its 

 expansions a rose-pink. 



LESSON III. 



HUMAN BLOOD CRYSTALS PROM BLOOD- 

 BLOOD PLATELETS. 



WRAP a twisted handkerchief round the ring-finger of the left hand, 

 and begin at the base of the finger, gradually constricting the 

 finger from the base towards the nail. The end phalanx will there- 

 by become greatly congested. With a sharp clean sewing-needle 

 prick the skin at the root of the nail ; a drop of blood will exude, 

 to which rapidly apply a slide ; cover the drop of blood on the slide 

 with a cover-glass, and examine it as quickly as possible. 



Observe various kinds of corpuscles floating in a fluid, the 

 blood-plasma or liquor sanguinis. Note the red and white cor- 

 puscles, the former being far more numerous. Blood platelets are 

 also present ; but it requires special precautions in order to preserve 

 them. 



1. Human Coloured Blood-Corpuscles (H). (a.) Observe the 

 field of the microscope crowded with the red or coloured disc-shaped 

 corpuscles much .smaller than those of the newt ; they are only 

 T-Vo^ 1 f an m( -h or 7-7 /* (l- 2 p-7'% A 1 ) i 11 breadth (p. 21), and 

 , ., ( ' MMT of an inch or 2 /A in thickness. The observer may notice 

 that when the corpuscles (-ease to move, after a time corpuscles may 

 be seen adhering to each other by their flat surfaces, until a chain 



