The difference of size in the corpuscles of different inninmalia is worthy of notice. The average diameter of those of man, according to Mr. Gulliver, is the 3300th of an inch ; but the average diameter of those of the elephant, according to the mine observer, is as much na the 2745th of an inch (which were the largest he observed amongst the nuninalia), whilst those of the Napu musk-deer were no more than the 12,325th, and some were an small an the 10,000th of an inch in diameter. There is also an exception to the general statement that the corpuscles of fishes are oval; in one class, namely the Cycloidomi, or. Lamprey Tribe, they aro circular. The largest rod corpuscles hitherto observed are amongst the reptiles known as the Syron and the Proteue, which are so large as even to be visible to the naked oyc ea very minute specks.
There can be no doubt that the red corpuscles go through the same course as other cells. We have undoubted evidence of their rapid regeneration in cases where much blood has been lost, and of the peculiar power which chalybeate medicines have in forwarding their production. The precise method in which they aro developed is however not exactly known.
With respect to the chemical composition of the blood-corpuscles, the walls are formed of a substance which has been called globulin, and which is undoubtedly ft protein compound. The red colour is due to a pigment which has received the name of Ilscinatin, and is inclosed in the vesicles of globulin. It has been generally assumed that this substance exists in two distinct states in arterial and venous blood, having in the former an excess of oxygen and in the latter an excess of carbon or carbonic add. Mulder has however shown that its elementary composition is the same whether obtained from arterial or venous blood, and that it may be represented by the formula C„11„ N, 0„ Fe; the following being the analyses from which he deduced it :— They are also to be distinguished from the red corpuscles by their different actions towards chemical re-agents ; they are not attacked by water, but remain in it for a long time without apparent change ; they are not rendered transparent and dissolved by acetic acid ; they only become more decidedly granular under its action, and a kind of nucleus is developed in their centre. As they are in all respects similar to those of lymph and chyle, and as they have the mune chemical relations, they have been regarded by many as the corpuscles of the lymph mingled with the blood (Hewson, Muller); others have viewed them as globules of coagulated fibrin (Mandl, Weber) ; and others again with more propriety as blood-corpuscles in progress of solution or disintegration (Wharton Jones, Hughes Bennett). They may be seen in the capillary system of living animals (in transparent structure*, an for instance in the frog's foot) swimming with the ordi nary blood corpuscles, but not so much moving rapidly in the great current of the blood as progressing in close contact with tho walls of the cowls in a slower stream. They. are not elastic like the ordinary corpuscles, and seem to stick to each other. The exact functions of these corpuscles are still unknown, but there are many facts which seem to indicate that there is a decided relation between thorn and between the nutritive or organic life of the tissues.
In addition to these cells, which as we have said are comparatively rare, an immense number of what are termed 'rod corpuscles, but which usually present a yellow appearance, are present in the red matter. The blood of numerous animals has been "submitted to microscopic examination by Name, Wagner, Gulliver, and other observers, and in general it is found that these red particles have a circular form In all animals constituting the clam Marnmalia. A remarkable exception to thin rule hen been shown by Mandl to occur in the corpuscle,' of the camel tribe. The mean long diameter of the blood-corpuscles+ of the Dromedary he found to be the 3254th of an inch, while the mean short diameter was only the 51121st of the same standard. In the Paco (A tichenia pare) and Guanaco (A achen i a Marna) the blood-corpuscles scarcely differed in form and size from those of the dromedary, whilst in the Vicufia they were slightly smaller. In structure and magnit tido however these oval corpuscles of the Cemelidir belong entirely to the mammifcrnus type ; they hare no perceptible It may be shown by conclusive experiments that the red colour is not dependent on the iron, for that constituent may be removed from the luematin without materially altering its tint, although it is very firmly combined with the four organic elements. The condition in which the iron exists in Immatin—wbether as an oxide, a carbonate, a carburet, or in the metallic state—has long been disputed. Accord ing to Liebig the iron of the hsernatin is the most essential constituent of the blood in relation to the respiratory process The following is his view of the theory of respiration :— " During the passage of the venous blood through the lungs, the globules change colour, and oxy gen is absorbed from the atmosphere. Further, for every volume of oxygen absorbed, an equal volume of carbonic acid is in most cases given out. The red globules contain a compound of iron, and no other constituent of the body contains iron. Whatever changes the other constituents of the blood undergo in the lungs, thin much is certain, that the globules of venous blood experience a change of colour, and that this change depends on the action of oxygen. Now we observe that the globules of arterial blood retain their colour in the larger vessels, and lose it only during their passage through the capillaries. All those constituents of venous blood which arc capable of combining with oxygen take up a corresponding quantity of it in the lungs. Experiments made with arterial serum have shown that when in con tact with oxygen it does not diminish the volume of that gas. Venous blood in contact with oxygen is reddened, while oxygen is absorbed, and a corresponding quantity of carbonic acid is formed. It is evident that the change of colour in the venous globules depends on the com bination of some one of these elements with oxygen ; and that this absorption of oxygen is attended with the separation of a certain quantity of carbonic acid gas. This carbonic acid is not separated from the serum ; for the serum does not possess the property when in contact with oxygen of giving off carbonic acid. On the contrary, when separated from the globules it absorbs from half its volume to an equal volume of carbonic acid, and at ordinary temperatures is not saturated with that gas. Arterial blood, when drawn from the body, is soon altered ; its florid colour becomes dark red. The florid blood, which owes its colour to the globule's, becomes dark by the action of carbonic acid, and this change of colour affects the globule's, for florid blood absorbs a number of gases which do not dissolve in the fluid part of the blood when separated from the globules. It is evident
therefore that the globules have the power of combining with gases. The globules of the blood change their colour in different gases ; and this change may be owing either to a combination or to a decompo sition. Sulphuretted hydrogen turns them blackish-green, and finally black ; and the original red colour cannot in this case be restored by contact with oxygen. Here a decomposition has obviously taken place. The globules darkened by carbonic acid become again florid in oxygen, with disengagement of carbonic acid. The same thing takes place in nitrous oxide. It is clear that they have here undergone no decomposition, and consequently they possess the power of combining with gases, while the compound they form with carbonic acid is destroyed by oxygen. When left to themselves out of the body, the compound formed with oxygen again becomes dark, but does not recover its florid colour a second time by the action of oxygen. The globules of the blood contain a compound of iron. From the never failing presence of iron in red blood, we must conclude that it is unques tionably necessary to animal life ; and since physiology has proved that the globules take no share in the process of nutrition, it cannot be doubted that they play a part in the process of respiration. The compound of iron in the globules has the characters of an oxidised compound, for it is decomposed by sulphuretted hydrogen, exactly in the same way as the oxides or other analogous compounds of iron. By means of diluted mineral acids, peroxide (sesqui-oxide) of iron may be extracted at the ordinary temperature from the fresh or dried red colouring matter of the blood. The characters of the compounds of iron may perhaps assist us to explain the share which that metal takes in the respiratory process. No other metal can be compared with iron for the remarkable properties of its compounds. The com pounds of protoxide of iron possess the property of depriving other oxidised compounds of oxygen ; while the compounds of peroxide of iron under other circumstances give us oxygen with the utmost facility. Hydrated peroxide of iron, in contact with organic matters destitute of sulphur, is converted into carbonate of the protoxide. Carbonate of protoxide of iron, in contact with water and oxygen, is decomposed ; all the carbonic acid is given off, and by absorption of oxygen it passes into the hydrated peroxide, which may again be converted into a compound of the protoxide. Not only the oxides of iron but also the cyanides of that metal exhibit similar properties. Prussian blue contains iron in combination with all the organic ele ments of the body ; hydrogen and oxygen (water), carbon and nitrogen (cyanogen). When it is exposed to light, cyanogen is given off, and it becomes white; in the dark it attracts oxygen, and recovers its blue colour. All these observations taken together lead to the opinion that the globules of arterial blood contain a compound of iron saturated with oxygen, which in the living blood loses its oxygen during its passage through the capillaries. The same thing occurs when it is separated from the body and begins to undergo decomposition. The compound, rich in oxygen, passes therefore, by the loss of oxygen, into one far less charged with that element. One of the products of oxidation formed in this process is carbonic acid. The compound of iron in tho venous blood possesses the property of combining with carbonic acid; and it is obvious that the globules of the arterial blood, after losing a part of their oxygen, will, if they meet with carbonic acid, combine with that substance. When they reach the lungs they will again take up the oxygen they have lost ; for every volume of oxygen absorbed, a corresponding volume of carbonic acid will be separated ; they will return to their former state, that is, they will again acquire the power of giving off oxygen. For every volume of oxygen which the globules can give off, there will be formed (as car bonic acid contains its own volume of oxygen without condensation) neither more nor less than an equal volume of carbonic acid. For every volume of oxygen which the globules are capable of absorbing, no more carbonic acid can possibly be separated than that volume of oxygen can produce. When carbonate of protoxide of iron by tho absorption of oxygen passes into the hydrated peroxide, there arc given off, for every volume of oxygen necessary to the change from protoxide to peroxide of iron, four volumes of carbonic acid gas. But from the one volume of oxygen only one volume of carbonic acid gas can be produced. And the absorptioh of one volume of oxygen can only cause directly the separation of an equal volume of carbonic acid ; consequently the substance or compound which has lost its oxygen during the passage of arterial into venous blood, must havo been capable of absorbing or combining with carbonic acid ; and we find, in point of fact, that the living blood is never in any state satu rated with carbonic acid ; that it is capable of taking up an additional quantity without any apparent disturbance of the functions of the globules. Thus, for instance, after drinking effervescing wines, beer, or mineral waters, more carbonic acid must necessarily be expired than at other times. In all cases where the oxygen of the arterial globules has been partly expended otherwise than in the formation of carbonic acid, the amount of this latter gas expired will correspond exactly with that which has been formed ; less however will be given out after the use of fat and of still wines than after champagne. According to the views now developed, the globules of arterial blood in their passage through the capillaries yield oxygen to certain con stituents of the body. A small portion of this oxygen serves to pro duce the change of matter, and determines the separation of living parts, and their conversion into lifeless compounds, as well as the formation of the scretions and excretions. Tho greater part, however, of the oxygen is employed in converting into oxidised compounds the newly-formed substances which no longer form part of the living tissues. In their return towards the heart, the globules which have lost their oxygen combine with carbonic acid, producing venous blood ; and when they reach the lungs an exchange takes ulace between this carbonic acid and the oxygen of the atmosphere. The organic compound of iron, which exists in venous blood, recovers in the lungs the oxygen it has lost, and in consequence of this absorption of oxygen the carbonic acid in combination with it is separated.