THE BLOOD. 41 



no way, as regards structure, distinguishable from the sub- 

 stance of the human blood disc, and the nucleus also being 

 identical in composition, though not in origin, with the 

 white globules of the blood, not merely of mammalia, but 

 likewise of reptiles, birds, and fishes. (See Plate II. fig. 5.) 

 The form of the nucleus, in the frog, &c., corresponds with 

 that of the globule; that is, it is elliptical (see Plate II. 

 fig. 2.): water, however, affects the nucleus, as first observed 

 by Mandl, in the same way as it acts upon the corpuscle 

 itself, rendering both perfectly spherical. (See Plate II. fig s. 

 3. and 4.) If to globules in this condition acetic acid be 

 added, the capsule will be dissolved, leaving intact the 

 nucleus, between which and a white globule I have not been 

 able to detect, although using an instrument of the very best 

 description, the slightest structural difference : a difference 

 does certainly exist, but it is one of size, and not of struc- 

 ture, the nucleus being three or four times smaller than a 

 white globule of ordinary dimensions. (See Plate II. fig. 5., 

 and Plate II. fig. 1.) This identity of organisation between 

 the white globule and the nucleus of the blood disc of the 

 frog, furnishes the strongest evidence with which I am ac- 

 quainted of the convertibility of the white globules into red, 

 evidence which, nevertheless, I regard as wholly inadequate 

 to demonstrate the reality of the conversion. 



Nucleus. The white corpuscles, under some circum- 

 stances, would appear to be nucleated; thus nuclei are 

 evident in corpuscles which have been immersed in water, or 

 even in serum, for any length of time, although they are not 

 usually seen in those of that fluid immediately after its 

 abstraction from the system. I am inclined to regard their 

 formation as resulting partly from the operation of endos- 

 mosis, whereby a portion of the contents of each corpuscle 

 becomes condensed in the centre. 



The nucleus occupies sometimes the entire of the interior 

 of the corpuscle, a narrow and colourless border, destitute of 

 granules, alone indicating the extent of the corpuscle ; gene- 

 rally, however, it is about the one third of its size, and is 

 more frequently excentric than centric. It is usually darker 



E 2 



