MICROSCOPIC EXAMINATION OF THE BLOOD. 3 



porarily, while thirst and the digestion of dry food raise it. If blood be passed 

 through an organ artificially, its specific gravity rises in consequence of the 

 absorption of dissolved matters and the giving off of water. It falls after 

 haemorrhage, and is less in badly-nourished individuals. 



2. Microscopic Examination of the Blood. 



[Blood, when examined by the microscope, is seen to consist of an 

 enormous number of corpuscles coloured and colourless floating in 

 a transparent fluid, the plasma, or liquor sanguinis.] 



The RED blood-corpuscles were discovered in frog's blood by Swam- 

 merdam in 1658, and in human blood by Leeuwenhoek in 1673. 



Characters of Human Blood (a.) Form. The human red blood- 

 corpuscles are circular, coin-shaped, homogeneous discs, with saucer-like 

 depressions on both surfaces, and with rounded margins; in other 

 words, they are bi-concave, circular discs. 



(b.) Size. According to Welcker the diameter (a b) is 7'7 /UL,* the 

 greatest thickness (c d) 1'9 jut. (Fig. 1, C) [i.e., it is 7r ^ nr to ^^ of 

 an inch in diameter, and about one-fourth of that in thickness]. 



The corpuscles are slightly diminisJied in size by septic fever, inanition, after the 

 subcutaneous injection of morphia, increased bodily temperature, and CO^ ; while 

 they are increased by O, watery condition of the blood, cold, consumption of 

 alcohol, quinine, hydrocyanic acid, and acute anemia (Manassei'n). 



A, Human coloured blood-corpuscles 1, seen on the flat; 2, on edge; 3, 

 rouleau of coloured corpuscles slightly separated. B, Coloured amphibian 

 blood-corpuscles 1, seen on the flat, and 2, on edge. C, Ideal transverse 

 section of a human coloured blood-corpuscle magnified 5,000 times linear ; 

 a b, diameter; c d t thickness. 



* The Greek letter n represents one-thousandth of a millimetre (u =0*001 mm.), 

 and is the sign of a micro-millimetre, or a micron. 



