102 ELEMENTARY PHYSIOLOGY lbss. 



substance of the corpuscle, is called the nucleus (Fig. 

 34, C) ; and when the blood is treated under the micro- 

 scope, with various staining fluids, such as solutions of 

 carmine or logwood, the nucleus generally stains more 

 deeply than the rest of the corpuscle. 



Such a colourless corpuscle as has been described, with 

 its nucleus, is what is called a nucleated cell. It will 

 be observed that it lives in a free state in the plasma of 

 the blood, and that it exhil)its an independent contracti- 

 lity. In fact, except that it is dependent for the conditions 

 of its existence upon the plasma, it might be compared to 

 one of th'se simple organisms which are met with in 

 stagnant water, and are called Aincalxp, whence the name 

 ' amoeboid ' given to the movements of the colourless cor- 

 puscles of blood. 



While the colourless corpuscles are thus nucleated cells, 

 the red corpuscles have no such nucleus ; and this is true 

 not only of human blood but of the blood of all mammals, 

 i.e. of all those animals which suckle their young ; in all 

 these the red corpuscle has no nucleus. In the case of 

 birds, reptiles and fishes, however, the red corpuscles as 

 well as the colourless are nucleated ; and in the embryos • 

 even of manmials the red corpuscles are at first nucleated. 



Whilst all the colourless corpuscles of the blood are 

 nucleated only about four- fifths of them have the power 

 of amoeboid movement. Those which have not this power 

 usually, but not always, possess a cell-body which is quite 

 clear and transparent. They are known as lymphocytes. 

 The cell-body of the majority more usually appears to be 

 granular from the presence in it of minute particles which, 

 varying in size, are spoken of as 'fine' or 'coarse.' We 

 may regard these particles as simply imbedded in the 

 ground-substance of which the cell body is made up, and, 

 since they are variable in size and numbers, as not essen- 

 tial to the structure of the corpuscle. What the real 

 sti'ucture of the living, contractile ground-substance or pro- 

 toplasm may be is still a matter of conjecture and dispute. 

 1 All embryo is the rudiuiLUtury unborn young of any creature. 



