104 Transactions of the Boyal Microscopical Society. 
The membraneous layer of the blood-corpuscle seems to be 
endowed with a certain degree of elasticity, manifesting itself in the 
expansion and contraction observed when the blood-corpuscle is 
subjected to the action of water or other reagents. AVhile the 
expansibility is but very slight, its contractility is considerable, as 
has been seen, when treated with a solution of hydrated chloral, 
chloroform liquid, or some other agents. While the protoplasm may 
be dissolved by water, dilute acetic acid, and some other reagents, 
it seems to undergo coagulation by the action of hydrated chloral, 
nitric acid, &c., assuming certain forms during this process. 
The nucleus represents an oval vesicle, containing most probably 
a more or less dense liquid with a- number of larger and smaller 
granules. After first expanding, these are finally dissolved by the 
action of water, causing at the same time a simultaneous increase 
in the volume of the whole contents, and an expansion of the wall 
of the nucleus. The liquid resulting from the dissolution of the 
granules may be rendered granular by the action of some acids. 
The nature of the granules and liquid contents of the nucleus is 
heterogeneous with that of the protoplasm of the blood-corpuscle, 
they being in most instances differently affected by one and the 
same reagent. 
The manifold changes of form which some blood-corpuscles 
undergo are due to a contraction of the protoplasm ; and as in 
almost every specimen of fresh blood some of these abnormal forms 
are met with, I am inclined to regard these changes as retro- 
gressive ; that is, as preceding the death or final disintegration of 
the blood-corpuscle. 
The Coloured Blood-corpuscles of the Frog {Bana pipiens ). — 
It is for the sake of comparison that I propose to enter into a dis- 
cussion of the structure of the coloured blood-corpuscles of this 
animal, a subject which has repeatedly been studied and discussed 
by almost every prominent histologist. The very fact that frogs 
are found in almsot every country where histological science is 
cultivated, and that their blood, being easily obtained, has thus 
become a common object for microscopical examinations, prompts 
me to demonstrate that the phenomena observed on the coloured 
blood-corpuscles of these animals differ but very little from those 
observed on the blood-corpuscles of the Amphiuma, and that it is not 
the enormous size of the latter which alone renders these phenomena 
so conspicuous to the observer. For this reason it cannot but 
appear strange that some of the most prominent points relating to 
the structure of these bodies should have passed entirely unnoticed, 
and furthermore that such palpable phenomena should have given 
rise to fanciful theories and speculations as mentioned in the intro- 
duction of this article. 
The coloured blood-corpuscles of the Frog resemble in form and 
