182 THE BLOOD 



employed for this purpose is a solution of sodium chlorid, the strength of which 

 must be varied somewhat in accordance with the type of the red cell to be pre- 

 served. Thus, it is best to employ it in strengths of 0.85 to 0.9 percent, for the 

 corpuscles of human blood and in a strength of 0.8 per cent, for those of ox blood; 

 in fact, the erythrocytes of the frog require an even weaker solution,' namely, 0.70 

 to 0.75 per cent. It should not be forgotten, however, that it is difficult to keep a 

 medium of this kind in a perfectly isotonic condition for any length of time, be- 

 cause a certain loss of water by evaporation cannot be avoided, and naturally, as 

 the solution becomes more concentrated, it incites such alterations as are usually 

 produced by hypertonic solutions of any kind. 



For purposes of transfusion a 0.75 per cent, solution of sodium chlorid, com- 

 monly designated as ''normal saline," is generally made use of. More favorable 

 results may be obtained at times by employing the so-called Ringer's solution 

 which contains the chlorids of sodium, potassium and calcium in the following 

 proportions : 



Sodium chlorid 0.9 per cent. 



Calcium chlorid . 026 per cent. 



Potassium chlorid ■ . 03 per cent. 



Under normal conditions, therefore, the blood plasma and the corpuscles are 

 in a state of osmotic equilibrium, and while water passes into them constantly, 

 an equal amount of the latter is again discharged into the plasma. In this way, 

 these two neighboring osmotic entities are enabled to retain the same concentration, 

 and hence, a destruction of the red cells cannot take place. But, naturally, if the 

 concentration of the plasma is either increased or decreased, the osmotic equilib- 

 rium is immediately disturbed. If increased, the plasma acts as a hypertonic 

 solution and if decreased, as a hypotonic solution. In either case, the change in its 

 concentration insures an alteration in its osmotic pressure, which immediately 

 gives origin to certain interchanges between it and the contents of the corpuscle. 

 Obviously, the purpose of this transfer is to reestablish an osmotic balance. Thus, 

 if the medium is hypertonic, molecules of water will continue to leave the corpus- 

 cles, until the latter eventually become greatly reduced in size and uneven in outline. 

 Conversely, a hypotonic medium will cause water to pass into the corpuscles 

 until they become much distended and finally rupture, giving rise to a great variety 

 of abnormal shapes. 



The red cells are regarded by some authors as small bags containing a concen- 

 trated solution of hemoglobin. The latter is said to diffuse out whenever the 

 enveloping membrane is changed in such a way that it becomes more permeable 

 to this substance. It must be doubted, however, that this explanation is correct, 

 because the red corpuscles do not possess a true cellular membrane enclosing a free 

 space, and because the hemoglobin actually forms an intricate part of the stroma. 

 Hence, the hemoglobin must first be separated from the latter, either by mechan- 

 ical or chemical means, before its escape from the cell can be effected. Obviously, 

 a red cell cannot be compared with a receptacle of water which, on breaking, 

 discharges its contents in all directions. 



In order to separate the stroma from the hemoglobin, it is best either to defibri- 

 nate the sample of blood or to render it non-coagulable by the addition of potassium 

 oxalate. It is then placed in the centrifuge. When completely separated, the 

 corpuscular elements are washed repeatedly in 10 to 20 volumes of a 1 to 2 per 

 cent, saline solution until free from serum. On addition of 5 to 6 volumes of dis- 

 tilled water containing a small amount of ether, ^ the corpuscles swell up and dis- 

 charge their hemoglobin into the surrounding medium. Centrifugalization is 

 resorted to in order to accelerate the deposition of the leukocytes. The supernatant 

 fluid is treated with a 1.0 per cent, solution of KHSO4 until it acquires the same 



1 Wooldridge, Archiv f . Anat. u. Physiol., 1881, 387. 



