to the same degree. At the same time that the envelope is becoming elongated, the nucleus undergoes a similar change, so that every part of the corpuscle becomes narrower than before, with the exception of the middle, which remains of the same size. During these changes, the concavity which was observed to exist in the second stage, in the space which intervened between the nucleus and border, is now seen gradually to disappear; at the same time that this change is going on, the borders, which were at that time like those of a guinea-piece, have now become rounded, so that there is a gentle convex declivity, (if I may be allow ed so to express myself,) between the nucleus and borders. The nucleus, during all the above changes, remains convex, and never presents a granular appearance subsequent to the first, and beginning of the second stages. I have never seen any opening in the centre of the nucleus, the envelope appearing to pass uninterruptedly over its surface. The envelope itself continues gradually to increase in strength from its first appearance, to the complete formation of the corpuscle.

It is stated in the above remarks, that the cytoblast of the blood corpuscle is seen to enlarge, and its central clear part to become granular, and that these two changes seem to depend on a process inherent in the body itself. This notion of the manner of formation of the above appearances, differs from that of most observers on this subject; for it is stated by them that it is caused by the joining together of numerous nucleoli contained in the blood. That this statement is not correct, the following cir cumstances clearly prove. At the time of the enlargement of the cytoblast, or cell-germ, its circumference is seen to be not scolloped, but smooth and regular. Now, this it could not be, if the enlargement depended on the aggregation of nucleoli. Again, at the time of the granular appearance of the central part, the nucleus is seen to be surrounded by a thin but distinct membrane, and that this membrane separates somewhat from the nucleus, during the time that body is becoming granular. These circumstances hinder us from believing that the granular appearance is caused by the junction of several independent granules to each other, whilst they entirely agree with the statements above made. This appearance is exactly similar to that discovered by Prévost and Dumas in the ova of frogs, and by Martin Barry in the ger minal spot of the ovum, during the development of these bodies. I do not state this merely from the plates of Martin Barry on this subject, but from the structure itself. I saw those granular or disc-like bodies so correctly described and illustrated by him, in the ova of a bitch, whilst assisting Dr Allen Thomson during last summer. Here I may state, that those divisions seen in the ovum were observed by Dr Allen Thomson a year previous to the publication of Martin Barry's papers in the Philosophical

Transactions, of which he made drawings, which he has now in his possession by him. I do not state this circumstance with the most distant intention of withdrawing from Martin Barry any of the credit which is due to him as the original discoverer. My design is to show, that there can scarcely remain any doubt as to the correctness of the description of the disc-like bodies seen in the developing ovum, as given by Martin Barry, when the same appearance has been seen by one of the best and most careful observers of the present day, and this the more especially, when these were made previous to the publication of the observations which they support. Dr Allen Thomson also observed, and made drawings of the granular appearance which the centre of the blood corpuscles present, in some stages of their development, some years since, when engaged in observing the development of the vascular layer in the embryo chick. With these I was wholly unacquainted, until after I had shown to Dr Thomson the observations above described, when he exhibited to me these drawings, representing correctly the granular appearance of the nucleus in its first stage of development.

For what end is this appearance designed? It appears to me to be the cause of the enlargement of the nucleus, and of nothing else. This opinion is different from that held by Martin Barry, for he states, "that the corpuscles of the blood are generated by a process essentially the same as that described in one of my former memoirs, as giving origin to those cells which are the immediate successors of the germinal vesicle or original parent cell;" and in the last paragraph of this paper are contained the following statements:" On a former occasion, I showed that the blood corpuscles are not formed, as supposed by some observers, out of the granules of the yolk. The facts recorded in the foregoing memoir leave little doubt, I think, that these corpuscles-not only in the embryo, but at all periods of life—are descendants of the two cells constituting the foundation of the new being in the ovum. If so, it is not requisite to seek the origin of these corpuscles in the organised parenchymatous substance of the body, or in the globules of the chyle, the only two sources, it has been said, "in which it was possible for them to arise." I am inclined to believe these statements to be incorrect, and that from the two following reasons: namely, that the granular appearance of the nucleus is only seen while that body is developing itself, this shape wholly disappearing when it has become fully formed; and from the fact that I have never seen these disc-like bodies, of which the nucleus, in its process of development, is composed, separate from each other, or escape from within the envelope of the blood corpuscle. If these three last state

1 Phil. Trans. 1840, p. 204.

ments be correct, it is clear that Martin Barry's assertion as to the origin of the blood corpuscle is erroneous.

In the foregoing observations it is said, that the membrane separates gradually from the nucleus. This separation does not take place in the manner generally described, namely, by a delicate transparent vesicle arising on the surface of each granule or cytoblast, in the form of a flat segment or sphere, like a watchglass on a watch; but by the separation of a membrane or ve sicle round the whole circumference of the cytoblast at the same time. This separation goes on gradually, and to the same extent round the whole surface of the cell-germ in the first and second stages; but in the third, one of its sides juts out, and then the other, until it has attained the oval shape of the fullgrown blood corpuscle of the chick. Struck with the great resemblance between the envelope of the blood corpuscle in its physical appearances, at its full development, as also in the different changes towards that end, with the basement or primary membrane of the ducts of the Wolffian bodies, with the sarcolemma of the muscular tissue, with neurilema of the nervous structure, &c. &c., I was led to examine into the structure and properties of these parts more minutely; and although my observations are not yet sufficiently extensive, to cause me to deduce from them with certainty any definite principle, yet so far as I have gone, I am led to believe that every or ganised substance in the animal kingdom is immediately surrounded by a pellucid and elastic membrane, having no fibres, vessels, or nerves in its structure, that it is acted on in the same manner, and to the same extent, in all situations, by acetic acid—and that in this membrane resides the property of eliminating or forming (?)2 from the blood the various structures in which reside the inherent properties of the different tissues, as likewise the secretions and excretions. If this general statement be cor rect, then the proper name for this structure, in all circumstan ces, as also in whatever shape it may present itself, will be the eliminative or formative membrane.

In the foregoing pages, it is observed, that we suspect the colouring matter of the blood to reside in the space between the nucleus and capsule. The data on which this suspicion rests are

1 I give these two terms out of justness to Mr Bowman and Mr Goodsir; as Mr Bowman, in his description of the mucous membrane, gave the first term to that structure, lying immediately beneath the epithelium; whilst Mr Goodsir, about the same time, and without any knowledge of these observations, gave the latter term to the same structure, seen in the uriniferous ducts of the kidney.

2 I use the mark of interrogation after the word " forming," because we have facts to prove that any organised structure has the power of changing chemically the ingredients of the blood. We have facts to prove that they afford circumstances for allowing changes to go on in the blood itself. We have none to show that there structures are the immediate cause of these changes.

as follow. At the time that the capsule closely surrounds the cytoblast, this body seems to be wholly deficient of any colouring matter, for let ever so many of these bodies, at this stage of development, be gathered together, they never present a yellow or reddish appearance, while as soon as that membrane or vesicle separates itself from the cell-germ to any extent, and a number of these bodies being at the same time close together, this yellow colour is seen. Moreover, this colour appears to take somewhat of a reddish hue, as the separation extends. From these facts, we are fully warranted to suspect, if not more than suspect, that the colouring matter resides in the situation above stated.

The appearances above described disagree in many points with those of Martin Barry, the latest writer on this subject. It is not my intention in the following remarks which I am about to make on his description of the blood corpuscle, to examine into the correctness of the opinion as to the immediate formation of various structures from these bodies. My design is to endeavour to prove that many of the appearances which he describes as belonging to the blood corpuscle in its natural state are incorrect. He states, at page 203 of the Philosophical Transactions for 1841, that "in all the blood corpuscles now referred to, which it will be seen are those of the four classes of vertebrated animals, including the two divisions of both reptiles and fishes, the nucleus has a cavity or a depression;" and further on he says, that "the corpuscle of the blood in certain states exhibits an orifice by means of which there is a communication with the exterior of the corpuscle and the cavity in its nucleus." In support of the above statement, Martin Barry brings forth the observations of De Torre, published in the Philosophical Transactions for 1766, p. 252, and before bringing these forward he premises them with the following sentence, "So little importance is attached in the present day to the observations of De Torre, that in a historical account of the blood corpuscle, I believe it is usual to pass them by as not deserving of notice, probably from an idea that his optical instruments were too imperfect; but I do not hesitate here to transcribe a passage from the observations of De Torre, although far from vouching for their entire accuracy." The following is that which he describes. "When any of the globules (blood corpuscles) happened to move with the serum in the most perfect focus, I could with great clearness distinguish the exterior and interior circumference of the ring of which each globule (corpuscle) consisted, the interior one being bounded by a black line or shade next the perforation exactly resembling that which bounded the exterior one. In such globules (corpus

This is not correct; Bostock, in his Physiology, mentions De Torre's observations succinctly but correctly.

cles) I could easily observe the ring articulated, the transverse lines at the joints being very distinguishable; the figures of the articulations were various, in some they were roundish, so that the rings appeared like a bead necklace, in others cylindrical, and of some length. The numbers of which the whole was composed seemed uncertain, varying from two or three to six or seven, many of the rings were broken, either by some confinement of the tales (talk) or by beating against each other, which I saw them continually do, and by these accidents the joints of the rings were detached, and wandered about separately in great numbers, and indeed they seemed separable with as much ease as if they had been united by mere contact only. Some of the rings were broken into semicircles, others into greater or less portions, others again divided into their constituent articulations, which, in some places, float about singly, or in others form, by their mutual attraction, a lateral union, like the pipes of an organ. I must observe, also, that these separated parts seem to be hollow and transparent, and like inflated bladders, and would easily yield and change their figures, stretching or contracting from round to oval and cylindrical, and vice versa, or any lateral pressure, in crowding them along with the serum, brought a constraint on them. Although the articulation was not distinguishable in every globule, I think it was so in the greater part of them, and it is natural to imagine that the rest were articulated likewise, though they might not pass at the proper distance for its being distinguished." The reason for transcribing the above long extract is, that we might have before us the principal statements of De Torre, whilst criticising his observations. The first thing that must strike every person who knows the history of the blood-corpuscle, and who reads the above quotation, is astonish ment at finding that any one, at this time of day, quotes the above statements of De Torre, believing that the greater part of them are correct. This astonishment must be increased tenfold when Martin Barry is known to be the believer. I have no hesitation in stating, that the appearances described by De Torre, when referred to the blood-corpuscles in their natural state, are erroneous. The basis on which the above assertion is founded, are the following facts, taken from De Torre's when compared with the acknowledged physical properties and appearances of these bodies in the present day. He states, in the paper above referred to," that many of the rings were broken, either by some confinement of the tale, or by beating against each other, which I saw them continually do; and by these accidents the joints of the rings were detached, and wandered about separately in great numbers, and indeed they ap pear separable with as much ease as if they had been united by mere contact only."

paper,

From this statement it seems very evident