10 RED CORPUSCLES 



Leucocytes are affected in much the same way as amoebae. 

 Their movements are notably arrested by the cinchona 

 alkaloids. Quinine injected into the circulation has been 

 found to diminish the migration of leucocytes from the 

 blood-vessels. 



Red Corpuscles are markedly affected by any change in 

 the salt content of the blood serum in which they are 

 bathed. These cells may be considered to be masses of 

 colloid material surrounded by a membrane, this membrane 

 being permeable by water, but having a selective power 

 with respect to the salts it will allow to pass through. 

 Blood serum normally contains 0*9 per cent, of sodium 

 chloride, and the corpuscles may be assumed to contain 

 the same amount. A salt solution of this strength is called 

 an isotonic solution, one of greater concentration is hyper- 

 tonic, a more dilute one being hypotonic. Red corpuscles 

 in an isotonic salt solution (' normal saline ') are unaffected, 

 for although osmosis takes place, the rates of diffusion, 

 in and out, are the same. Cells placed in a hypotonic 

 solution swell up, for salt diffuses out of them and water 

 enters until the envelope, no longer able to contain the extra 

 fluid, bursts, setting free the haemoglobin. If the cells are 

 placed in a hypertonic salt solution, water diffuses out to 

 dilute the more concentrated fluid, while salt diffuses in, 

 but the net result of the loss of fluid from the cell is that it 

 shrinks and becomes crenated. Thus any excess of water 

 in the blood serum at once results in an increase in the size 

 of the red cells, which imbibe fluid, swell up, and burst. 

 On the other hand, if an excess of salt (sodium chloride) is 

 put into the bloodstream so that the serum becomes hyper- 

 tonic, water diffuses out of the red cells to dilute the serum, 

 the red cells becoming smaller and shrivelled, or crenated. 



The important blood constituent haemoglobin, like proto- 

 plasm, has great capacity for taking up oxygen, thus 

 becoming converted into oxy haemoglobin, which, however, 

 holds its added oxygen loosely, and parts with it readily, 

 as it slowly circulates through capillary vessels. The haemo- 

 globin also combines with other substances as well as with 

 oxygen as with hydrocyanic acid and carbon monoxide, 

 forming tolerably stable compounds ; and these can neither 



