70 Transactions of the Royal Microsco 2 ncal Society. 
expansion of this substance, accompanied by a corresponding dis- 
tension of the membraneous layer, causing in many cases a rupture 
as above stated. At this time the density of the protoplasm is still 
sufficiently high for keeping the nucleus in its normal place, the 
centre. But by the continued action of the water upon the proto- 
plasm, the density of the latter gradually diminishes until, in virtue 
of the law of diffusion, it is rendered equal with that of the 
surrounding fluid. As soon as the rupture occurs, therefore, the 
distended membraneous layer, being now relieved from its pressure 
by an escape of a portion of the fluid within and through the orifice 
produced by the rupture, commences to contract. Now it is that 
the nucleus is seen to leave the centre and to approach the inner 
surface of the membraneous layer. Finally, by the continued con- 
traction of this layer it arrives at the orifice, through which it is 
slowly pressed. It is owing to this process that a considerable 
number of free nuclei are always met with when the blood of the 
Amphibia is treated with the water. And as no contour of the 
main body of the blood-corpuscle can be discovered around them, it 
might appear as if the whole, except the nucleus, had been dissolved 
by the reagent. 
In accepting the view of those histologists who deny the 
existence of an enveloping membrane of the nucleated coloured 
blood-corpuscle, and supposing it to consist only of a homogeneous 
protoplasm throughout surrounding the nucleus, it becomes difficult 
to explain in a satisfactory manner the phenomenon just described. 
Kollett, in his article “ On the Blood,” in Strieker’s ‘ Handbucli der 
Lehre von den Geweben, &c.,’ also mentions the above-described 
phenomenon observed on the nucleated blood-corpuscles, but omits 
to offer any explanation. And indeed, maintaining, as he does, the 
idea that the body of the blood-corpuscle consists of a certain 
stroma determining its form, and insoluble in water, I cannot 
conceive of any rational explanation which he could offer. As the 
nucleus occupies the centre of the stroma, it of course cannot 
become displaced as long as the consistence of the stroma remains 
unafiected by the water, unless the stroma itself is torn or loses its 
integrity in some way or other in that direction in which the 
nucleus moves. But then the question remains to be answered: 
What is the force that displaces the nucleus ? Is it a spontaneous 
contraction of the stroma ? If so, the nucleus would only be em- 
braced the firmer, unless a rupture of the stroma occurs, allowing 
it to escape. But it does not always escape, as Eollett states him- 
self ; it is only displaced from the centre to an excentric position. 
Therefore, admitting even that the nucleus is able to assume an 
excentric position when surrounded by a homogeneous substance of 
a certain consistence, as this stroma must certainly be in order to 
preserve the form of the blood-corpuscle, the question remains 
