BLOOD. 5 



Note. The osmic acid and picrocarmine, and osmic acid and logwood preparations of 

 blood are the only permanent preparations which show colourless corpuscles. A careful search 

 is sure to reveal several corpuscles with their nuclei stained. 



In fresh blood an eighth-of-an-inch lens shows the intra-nuclear plexus of fibrils in the 

 colourless corpuscles. 



(B.) HUMAN BLOOD. 



PREPARATION. Wrap a handkerchief tightly round a finger, beginning at the base and 

 proceeding towards the point, which will cause the point of the finger to become congested ; 

 then prick the skin at the root of the nail with a clean sewing needle and bring a slide in con- 

 tact with the drop of blood which exudes. Apply a cover and examine. 



EXAMINATION. i. Observe the coloured corpuscles (H). At first the coloured blood- 

 corpuscles will be seen adhering by their flat surfaces so as to form rouleaux. These piles 

 may form a kind of network. {Indicate these rouleaux in PI. I., Fig. 9.) When so disposed 

 it is of course their edges only that are seen ; but if the cover be gently moved with a 

 needle-point, the rouleaux break up, and then the individual corpuscles are seen both on 

 the flat and on edge. On the flat they appear as bi-concave, circular discs ; while edge- 

 wise they appear somewhat dumbbell-shaped (PI. I., Fig. 10). On carefully focussing a 

 corpuscle as seen on the flat, a dark part at first appears in the centre, the margin being 

 light (PI. I., Fig. u); but on altering the fine adjustment the centre becomes light, and 

 the circumference dark (PI. I., Fig. 11). These changes in appearance are due to the fact 

 that the corpuscle is a bi-concave disc. It is not due to the presence of a nucleus, for 

 these corpuscles are non-nucleated and homogeneous throughout. It is well to become 

 familiar with the size of a corpuscle seen under a power of 300 diameters, for a corpuscle so 

 magnified serves as a useful standard of comparison for other objects. The diameter of a 

 corpuscle is 3 ' inch. It is generally stated that the coloured corpuscles are all of the 

 same size, but this is not strictly correct, for a careful examination shows that there is a 

 slight variation from this standard, and this variation is greater in some individuals than in 

 others, and becomes specially marked in some diseases. 



EFFECTS OF REAGENTS, (a) Acetic Acid. When irrigated with one per cent, dilution 

 of acetic acid, the coloured corpuscles become globular and lose their colouring matter, which 

 diffuses into the surrounding fluid, so that it is difficult to distinguish the outline of the indi- 

 vidual corpuscles. No nucleus is revealed. 



(K] Water. Irrigation with water decolourises the corpuscles and renders them globular. 

 The colouring matter is dissolved by the water which passes into the corpuscles by endosmosis 

 and renders them globular. The surrounding fluid becomes yellowish in colour. 



(c) Tannic Acid. If a drop of blood is -mixed with a two per cent, solution of tannic acid 

 (p. 2), one or more small refractive buds are seen to appear on the margins of the corpuscles. 

 These buds are produced by the same causes that produce similar buds on the corpuscles of 

 the newt. 



(ef) Common Salt. When blood is irrigated with a two per cent, solution of common salt, 

 crenation of the coloured corpuscles takes place that is to say, they become jagged at the 

 margins and on the surface, so that they resemble small thorn-apples. At the same time, the 

 corpuscles gradually become smaller and deepen in tint, but all the corpuscles are not affected 

 to the same extent or with the same rapidity. Perhaps this difference in the action of the 



