THE BLOOD 243 



The Preservation of the Red Corpuscles in the Plasma. Within the 

 blood-vessels the physical conditions and chemic composition of the plasma 

 are such that both the form, and the composition of the corpuscle or the rela- 

 tion of the hemoglobin to the stroma, are maintained in the normal or physio- 

 logic condition. The plasma is preservative of the structure and function 

 of the corpuscle. The reason assigned for this is that the osmotic pressure 

 of the salts in the plasma and of the salts in the corpuscle exactly balance 

 one another so that there is neither an absorption of water from, nor a yield- 

 ing of water to the plasma, on the part of the corpuscle. The plasma having 

 an osmotic pressure equal to that within the corpuscle is said to be isotonic 

 with it. 



When blood is to be prepared for microscopic examination with a view of 

 determining the histologic features of the corpuscles or for purposes of 

 enumeration, it must be diluted, and unless special precautions are 

 observed the condition of equal osmotic pressure will be disturbed by the 

 diluting agent and the corpuscles will lose their characteristic form and 

 structure from either an absorption or loss of water. 



If distilled water is employed for this purpose, the osmotic pressure of the 

 plasma is of course diminished, and in consequence the osmotic pressure of 

 the inorganic constituents of the corpuscles (particularly potassium phos- 

 phate) causes an inflow of water. The corpuscle therefore swells and 

 assumes a more or less spheric form; the hemoglobin is dissociated and 

 discharged into the surrounding fluid throughout which it diffuses. Such 

 an environment having an osmotic pressure less than that of the corpuscle is 

 said to be hy polemic > or hypo-isotonic to it. 



If on the contrary, water containing inorganic salts (particularly sodium 

 chlorid) is added in amounts which impart to the plasma an osmotic pressure 

 greater than that within the corpuscle, there will be an outflow of water 

 from the corpuscle, a shrinkage of the volume and a crenation of its surface. 

 Such an environment having an osmotic pressure greater than that of the 

 corpuscle is said to be hypertonic, or hyperisotonic to it. It is essential 

 therefore in diluting the plasma with water, that the latter contains inorganic 

 salts in such amounts that the resulting mixture (plasma and water) possesses 

 an osmotic pressure equal to that of the original plasma or to that of the cor- 

 puscle. A diluting agent well adapted for this purpose is the well-known 

 Ringer's mixture. Other solutions which preserve the form of the corpuscles 

 during the time required for their enumeration are the solutions devised by 

 Hayem, Toisson, and G owers alluded to on a preceding page. Because of the 

 fact that sodium chlorid is the chief inorganic constituent of the plasma it is 

 common in laboratory work to dilute the plasma of mammalian blood and 

 of frog's blood with solutions of sodium chlorid of 0.9 per cent, and 0.6 per 

 cent, respectively, which though not absolutely are sufficiently isotonic for 

 the purpose desired. 



The Effects of Reagents. Many other saline solutions with an osmotic 

 pressure greater or less than normal plasma, dilute solutions of acids and 

 alkalies, bile salts, chloroform, ether, ammonium sulphocyanid, electricity, 

 etc., also destroy the physical and chemic integrity of the corpuscle and cause 

 the hemoglobin to separate from the stroma and diffuse into the plasma 

 without itself undergoing any appreciable change in composition. With 

 the escape and diffusion of the hemoglobin the blood becomes transparent 



