THE BLOOD. 



683 



monkey's blood, human lachrymal or nasal secretion, being eliminated, a positive reaction 

 with the serum-test is strong evidence of the presence of human blood. • 



The nonnucleated condition of the mature erythrocytes is the distinguishing characteristic 

 of mammalian blood as contrasted with the colored corpuscles of other vertebrates, since even 

 in the exceptional oval red cell of the camel family the nucleus is wanting. The mammalian 

 red corpuscles, however, must be regarded as a secondary deviation from the fundamental type 

 represented by the oval nucleated erythrocyte of the other vertebrates, the nucleated embryonic 

 red cell losing its nucleus as maturity is acquired. In general, the oval nucleated red cells are 

 larger than the mammalian nonnucleated discs. The largest erythrocytes are found in the 

 tailed amphibians; those of the amphiuma, the largest known, attain the gigantic length of .080 

 mm. , and are approximately ten times as large as the human red blood-cell. 



The structure of the red blood-cell has long been and still is a subject of dis- 

 cussion, two opposed views finding ardent supporters. According to the one, held 

 by Schaefer,^ Weidenreich, and- others, the erythrocyte consists of a membranous 

 external envelope inclosing the colored fluid contents. On the other hand, RoUett 

 and many others regard the corpuscle as composed of an insoluble flexible spongy 

 stroma of great delicacy, occupied by the coloring matter or hemoglobin. Although 

 no definite envelope is present, in the sense of a distinct cell-membrane, it is highly 

 probable that a peripheral condensation of the stroma exists. The fact that the 



A. 



Fig. 647. 



B. 



Nucleated amphibian red blood-cells; A, from newt ; B, from amphiuma. X 750. 



fragments into which the red blood-cells may be broken up after certain treatment, 

 as by heating, retain the appearance and structure identical with the larger original 

 cell, is strong evidence that the hemoglobin has not escaped and, therefore, does 

 not exist in a fluid condition within the cell, notwithstanding the ingenious but 

 scarcely convincing explanations of the phenomena advanced by the supporters of 

 the vesicular structure of these cells. Further, the evidence afforded by those 

 parts of the corpuscles that remain after abstraction of the hemoglobin by water, 

 ether, and other reagents, points to the existence of a distinct stroma, the thicker 

 edges of which appear in profile as outlines of the "ghosts" that then represent 

 the former colored cells. 



The erythrocytes are extremely sensitive to a wide range of reagents and conditions and, 

 therefore, require great care in their collection and examination if distortions are to be avoided. 

 Exposure to even a current of air often suffices to produce conspicuous changes in the red blood- 

 cells. Alterations in form may be grouped into those resulting from the action of solutions of 

 lower and of higher density than that of the normal plasma. The latter is conveniently sub- 

 stituted by an .85 per cent, solution of sodium chloride. If the proportion of salt be grad- 

 ually reduced, the corpuscles show evidences of swelling, at first by losing their concavity on 

 one side and later, as the density of the reagent approached that of water, assuming the 

 spherical form and parting with the hemoglobin and becoming colorless. On the other hand, 



^ Anatomischer Anzeiger, Bd. xxvi., 1905. 



