PRACTICAL HISTOLOGY. 



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 BLOOD. 



WHEN examined microscopically blood is seen to contain corpuscles floating in a fluid the 

 plasma or liquor sanguinis. The corpuscles are of two kinds, (i) coloured and (2) colour- 

 less, and in addition (3) minute granules are to be seen. Besides these, there fall to be 

 examined (4) the fibrin and (5) the colouring matter of the coloured corpuscles and (6) 

 various pigments derived therefrom. 



(A.) BLOOD OF A FROG OR NEWT. 



PREPARATION. Give a frog or newt a smart blow on the head. If a newt be 'taken, 

 carefully wipe its tail dry by means of a cloth and snip off the point of the tail. Then 

 squeeze out a drop of blood from the stump on to a glass slide, and at once apply a cover- 

 glass. If a frog be used a toe should be cut off, when a drop of blood can easily be squeezed 

 out of the stump. In either case the blood thus obtained will be mixed with a considerable 

 quantity of lymph. If a drop of blood without any admixture of lymph is required, the heart 

 of the animal must be exposed, and when this is done the auricle should be snipped through 

 and a drop of blood allowed to fall on the glass slide. 



EXAMINATION. i. Observe the coloured corpuscles (H). They are seen to be very 

 numerous, of a yellowish straw colour, uniform in size and elliptical in shape when seen on the 

 flat (PI. I., Fig. i).* A few of them may also be seen edgewise, and they then appear narrow, 

 somewhat pointed at the ends, and slightly thicker in the middle (PL I., Fig. 2). Sometimes 

 one corpuscle lies above another, when the outline of the undermost one may be distinctly 

 seen through the one lying above it ; it is thus seen that each corpuscle is transparent. 

 At first each corpuscle may seem homogeneous, but in a very short time an elliptical slightly 

 granular body shows itself in the centre of each as seen on the flat. This body, which is 

 somewhat lighter in colour than the rest of the corpuscle, is called the nucleus (PI. I., Fig. i). 



EFFECTS OF REAGENTS on the coloured corpuscles. 



(a) One per cent. Hydrochloric Acid. Squeeze out a fresh drop of blood on a clean slide, 

 quickly apply a cover-glass, and then place a drop of a one per cent, dilution of hydrochloric 

 acid at one edge of the cover-glass (taking care that none of the acid gets on the top of the cover- 



Whei^e a simple reference is made to a plate and figure (as PI. I., Fig. i), it is intended that the student shall insert 

 by delineation and colouring such appearances and changes as are indicated in the text as the result of reagents or otherwise. 



