376 THE BLOOD, BY ALEXANDER ROLLETT. 



able appearances, that statements based upon mere analogy can 

 only be received with the most profound distrust. 



The results that have been obtained by direct observation 

 and inquiry will therefore here first be given, in order that we 

 may not become confused with theories that have been incon- 

 siderately advanced ; the views of various histologists, founded 

 on their own investigations, will* however, be subsequently 

 noticed. 



FORM AND COLOUR. Throughout the whole series of ver- 

 tebrate animals two typical forms are presented by the red 

 blood corpuscles. They form thin disks, the contour of which 

 is either circular or elliptical. The circular disks occur in Man 

 and Mammals, with the exception of the Camel and Auchenia. 

 The two last-named genera have, like all Birds, Amphibia, and 

 most Fishes, elliptical blood corpuscles. 



Amongst the Fishes only a few Cyclostomata (Petromyzon, 

 Ammocostes) are known to possess circular disks. 



A small drop of human blood, brought as quickly as possible 

 under the microscope in the form of a thin layer, exhibits 

 densely crowded coloured corpuscles. 



Their colour depends upon haemoglobin* The individual 

 corpuscles, however, do not appear red like pure haemoglobin, or 

 its concentrated solutions, but of a yellowish or green tint, per- 

 haps on account of its small thickness, just as the same colour 

 may be obtained if thin layers of concentrated watery solu- 

 tions, or thick layers of diluted solutions, of haemoglobin are 

 examined, and this whether it be oxy haemoglobin or reduced 

 haemoglobin, or a definite mixture of both. The red colour of 

 the blood is only exhibited under the microscope when large 

 numbers of blood corpuscles are examined superimposed on one 

 another. 



Where a number of the corpuscles thus lie upon one another, 

 as may occur by chance in every small drop of blood, there 

 may also be seen, as F. Hoppe, f Preyer, + and Strieker 



* Compare Kiihne, Lehrbuch der Physolog. Chemie. Leipzig, 1866, p. 196. 

 t Virchow's Archiv, Band xxiii., p. 446. 

 t Max Schultze's Archiv, Band ii., p. 92. 

 Pfliiger's Archiv, 1868, p. 651. 



