RED CORPUSCLES OF THE BLOOD. 575 



very gradually, as often occurs in the blood of cold-blooded 

 animals ; or if larger quantities of fibrin quickly separate, the 

 whole drop of blood solidifies, without any alteration of the 

 microscopic appearances being perceptible. In this case the 

 change that has occurred only becomes evident on moving or 

 breaking up the mass when it has undergone coagulation. 



If, on the other hand, we leave a few drops of blood for a 

 little while to themselves, which may be best effected by at- 

 taching them to the under side of a glass cover in a moist cell, 

 we shall observe that the coagulum embracing the corpuscles 

 retracts from the borders of the drop, and that a zone of clear 

 serum is exuded, which gradually increases in breadth. 



Here also striae and bands of coagulated fibrin may be iso- 

 lated by breaking up the coagulum and thorough elutriation 

 with water. 



The fibrinous coagulum appears doubly refractile under the 

 polarising microscope. 



We shall hereafter revert to the behaviour of the blood cor- 

 puscles in the fibrinous coagulum. 



THE RED BLOOD CORPUSCLES. A knowledge of the general 

 structure of these bodies cannot here be discussed, but will be 

 taken for granted in the course of the following observations. 



After the blood corpuscles had once been seen by Swammer- 

 dam in the Frog in 1658, by Malpighi in the Hedgehog in 

 1661, and by Leeuwenhoek in Man in 1673, numerous observa- 

 tions were accumulated respecting them, perhaps even to a 

 greater extent than upon any other* morphological element of 

 the animal body. Up to the present time, however, no struc- 

 tural arrangements have been discovered in them with the 

 microscope that can enable us to furnish an explanation of all 

 or even of the greater number of the phenomena they display. 



Compared with other morphological elements of the tissues, 

 the red blood corpuscles appear so peculiar, and are so readily 

 and permanently alterable by the action of numerous and often 

 not obvious external influences, and present so many remark- 



* For the older literature, see Milne Edwards, Lemons sur la Physiologie 

 et VAnatomie comparee. Paris, 1857, T. i., p. 41. 



