64 Transactions of the 



however, do not seem originally to have belonged to the meshes ; 

 but, on the contrary, have carried them by manipulation, as it is 

 impossible to remove even the smallest portion of the pulp without 

 cutting at the same time some of the finer blood-vessels, from which 

 these coloured blood corpuscles are derived. 



The mode of multiplication of the above-named elements does 

 not take place, according to my own observations, by a direct 

 division of the nucleus. The process of multiplication can there- 

 fore only be explained by looking upon those nucleated cells as the 

 birth-place of the free nuclei. These cells possess a membrane, 

 indicated by their double contour, and can therefore not be regarded 

 as colourless blood corpuscles. It is more probable that they repre- 

 sent breeding cells, and that the nuclei within them were produced 

 by the endogenous formative process, to be eventually set free. A 

 number of them may, after being set free, be developed into breed- 

 ing cells, while the rest, at first surrounded by a thin layer of 

 protoplasm, escape from the meshes of the pulp into the circulation 

 of the blood, to commence their career as colourless blood corpuscles. 

 In the course of their development the layer of protoplasm increases 

 in thickness, and the nuclei obtain their subsequent smooth appear- 

 ance by the disappearance of the granules within them. This 

 explanation coincides also with the results of my observations on 

 the spleen of the human embryos above mentioned, where I met 

 with the elements just described. 



In examining the colourless blood corpuscles of the chculating 

 blood of man in their fresh condition, it is quite as impossible to 

 discover on them an enveloping membrane as on the coloured ones. 

 On the addition of water, however, their protoplasm becomes pale, 

 and of a homogeneous appearance, and appears, with certain excep- 

 tions, to be bounded by a very delicate double contour. In conse- 

 quence of this change, the homogeneous disk-shaped nucleus, which 

 in some cases also shows a fine double contour, becomes more 

 sharply defined. The colourless corpuscles of the fresh blood appear 

 different in size and form, and even in their behaviour in relation 

 to external influences. The differences in the size of these bodies 

 seem to depend mainly upon the thickness of the layer of proto- 

 plasm surrounding the nucleus, in consequence of which this layer 

 is very thin on the smaller corpuscles, which most probably repre- 

 sent the younger specimens. The amoeboid movements observed in 

 this protoplasm do not occur regularly in all colourless corpuscles 

 of the same blood. In the smaller and younger ones, therefore, 

 they are more rarely observed than in the larger and matured ones. 

 In some cases, these movements appear immediately after the fresh 

 drop of blood is brought upon the slide, in others, again, only after 

 the addition of some water. Equally as indefinite is the length of 

 time during which they are seen to occur. This noticeable difierence, 



