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moment, in any part of the great current of the circulation, simply because they are taken up, and used, in the work of conversion and construction almost as rapidly as they are supplied. If they were the final issues, instead of being the material means of the constructive operation, as it will be presently seen their associates the coloured blood-corpuscles are, they would be as numerous as those little crimson bodies. Wherever the hurrying blood gets into channels that retard its onward flow the colourless corpuscles become immensely more abundant, because then their multiplication is continued while their expenditure is arrested. In the extreme capillary channels of the circulation, where the constructive energies of the colourless corpuscles have to be mainly exerted, the motion of the bloodstream is of necessity slow, because the actual area of this terminal network is of some four or five hundred times larger capacity than the area of the main vessel which furnishes the supply. The current of the blood waxes slower and slower as it passes on into the larger space that is laid out for its conveyance. It will be at once perceived how admirably this retardation of the movement of the blood in the minute channels of the circulation, where it is virtually brought into close contact and connexion with the fabrics that are to be operated upon, favours the proceedings of these subtle little fabricators, the colourless corpuscles.

The coloured corpuscles of the blood are, however, of a very different nature to their colourless allies and associates. So long as they are engaged in the work of energetic and rapid multiplication the colourless corpuscles are without any trace of external investment of formed substance. They are merely corpuscular aggregations of bioplasm, and in no sense vesicles, or cells. They only put on the external investment of formed substance, and assume the true vesicular condition, when they are passing on from the state of active life into the state of formed texture—when they are ceasing to be constructing agents, and are getting to be constructed material. The coloured blood-corpuscles, on the other hand, are more of the nature of vesicles from the very first. The molecules of coloured liquid, of which they chiefly consist, are at all times enclosed within a delicate investment of formed substance. Most probably the small mass of bioplasm, that sets to work to construct this investing coat for itself, is but a variety of the young colourless corpuscle. Colourless corpuscles, formed out of living bioplasm, grow, multiply, and pass on into the developed state of coloured corpuscles.

The coloured corpuscle is not only of a somewhat smaller VOL. CXXXVI. NO. CCLXXVII.

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size than its pale companion and ally, it is also of an altogether different form and aspect, and is entirely devoid of capacity of intrinsic vital movement. It is swept along in the general · current of the blood-stream, and is sometimes a trifle more distended, and at other times a trifle more pressed in. But it exhibits none of the internal unfixedness and restless change of shape that have been spoken of as the leading characteristic of the colourless corpuscle. It is, indeed, an already fixed and fully-developed vesicle-like body, fashioned for particular work, and on that account left with a lower endowment of vital energy. The general shape of the outer envelope is not spherical, but lenticular, compressed in one direction from side to side. As it is rolled along in the channels of the circulation it presents itself sometimes sideways, and sometimes edgeways, to the eye. The sides are not smoothly and evenly curved, but slightly dimpled in the middle, so that they look as if they consisted of a central darker spot and a surrounding ring of lighter hue. The investing coat is soft, flexible, and elastic, and capable of yielding readily to the impression of external force, although destitute of all power of independent movement. The substance contained within is a thick crimson fluid somewhat of the nature of highly plastic fibrin, but most probably of still more elaborate and finished character, and is strongly impregnated with iron.

The question of the actual character and parentage of the red corpuscle, and of the early relationship and affinities of the two corpuscles—the colourless and the coloured—is perhaps not yet absolutely settled. There are, for instance, experienced and accomplished physiologists who believe that the red corpuscle is formed in the interior of the colourless corpuscle by the development and maturation of a nucleus,' and that the colourless corpuscle is invested by a cell-film, which is burst when the young red corpuscles are thrown loose into the bloodstream. Yet others maintain that the red corpuscle is a porous mass of dead formed structure, containing in its pores coloured living pulp (oecoid and zooid of Professor Brucke), and that the living pulp can be caused to move bodily out of the containing pores by certain physical influences. Making all due allowance for the aberglaube' complexities of this subtle department of physiological investigation, there remains, however, safe ground for the conclusion that the colourless bloodcorpuscle is a formative body of high vital endowment and activity, and that the red blood-corpuscle is a formed body, fabricated from aggregations of bioplasm by development and transformation. Day by day, the notion that bioplasm accomplishes most of the broadest functions of organisation, and that

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it is seen so performing them in the case of the colourless corpuscles of the blood independently of vesicular construction of any kind, and that vesicular formation is altogether a secondary, independent, and ulterior result, is gaining stronger acceptance among physiologists.

The enormous abundance of the coloured blood-corpusclesthe countless millions of them which are contained in the streaming circulation of a single individual, and which are being reproduced generation after generation in unceasing succession, from the period of birth to that of final dissolution at the end of the natural term of existence-sufficiently indicates what important agents these bodies are in the economy and operations of animal life. In all probability they contribute, in some degree, to the actual formation of organised structure. But this is not their chief business and purpose; they clearly have a more direct and special commission of usefulness in the living scheme. The coloured corpuscles act specially as carriers of influence, and as equalizers and regulators of condition. They rouse and sustain vital energy and power, and they keep the blood in the precise state in which it is required to be for the manifold offices it has to accomplish. They convey from the lungs the aerial influence—the oxygen-which enters there in the act of respiration, and bear it to the minute capillary channels of the circulation, where its chemical influence has to be exerted in the evolution of animal warmth, or blood-heat, and in sundry other transforming operations connected with the presence of impulse and effort. The particular powers of muscle, nerve, and brain---the most highly endowed parts of the living apparatus—are unquestionably stimulated and maintained in their fullest energy and perfection by the instrumentality of the red corpuscles.

A considerable portion both of the oxygen gas acquired in the lungs, and of the carbonic acid gas generated in the capillary extremities of the circulation, is at all times mingled with the blood in the disengaged gaseous state. The blood contains as much as half its own volume of free gas. In 100 cubic inches of blood there are 50 cubic inches of gas, of which one-third is oxygen on its way to the structural penetralia of the frame, to perform there its office of resolution and reduction of complex principles; and two-thirds are carbonic acid gas on its way from these penetralia, where it has been generated by the resolving power of oxygen, to the pulmonary and other outlets, whence it has to be discharged at once, not only from the blood, but also from the body. About one-tenth of the free gas in the blood is nitrogen, an element whose presence is less perfectly

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understood. It is a remarkable fact that the blood holds suspended in its liquid substance a very much larger proportion of uncombined oxygen than pure water can contain. This is mainly due to the action of the coloured blood-corpuscles. The red liquid of these little bodies has the power of holding comparatively large quantities of gaseous oxygen in a grasp so close that it nearly resembles the strong embrace of chemical affinity, and yet so light that the chemical integrity and individuality of the agent are not placed in abeyance or interfered with. Some highly oxydisable principles, which are readily corroded by oxygen in other circumstances, pass unscathed with it through the blood in its progress through the frame, on account of the stronger hold exerted upon it by the ferruginous liquid of the corpuscle.

Oil, derived from the digestion of the fatty ingredients of the food, is always present in the blood in considerable quantity. There is nearly half an ounce of oil in fifteen pounds of blood. A portion of this oil is mingled with the serous liquid. Other portions are mingled very closely and intimately with the crimson liquid of the red corpuscle, and, therefore, belong to the corpuscular rather than to the serous part. The oilspherules of the serum are used up as fuel in the production and maintenance of animal heat. The oil of the bloodcorpuscles, on the other hand, is devoted to constructive, and not destructive, work. It is largely used in the fabrication of nerve and brain, and more moderately in that of some other textures.

The constitution of the blood, which has thus been passed in review, is a subject of deep and absorbing interest when looked upon merely as a matter of intelligent inquiry. Upon that ground alone the somewhat elaborate discussion of the subject which has been hazarded might almost be excused and justified. But there is a very much stronger reason for the procedure, which has now to be developed and urged. The observation and study, and the intelligent apprehension of the composition, of the blood is not only a piece of piquant intellectual enjoyment, it is also a matter of practical wisdom, and, it may perhaps also be added, of responsible duty, for every individual who forms part of the great scheme of social human existence. For it is in the derangements of the adjustments which have been spoken of in the preceding pages that the cause of the vast array of physical evils, which bear the collective name of Disease, has to be looked for; and it is by a rational apprehension on the part of the general community of the light which science has been able to throw upon their insidious ope

baneful power:

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rations that their fell agency in shortening the appointed span of life can be most surely counteracted and deprived of its

That a considerable number of what are termed zymotic, or infectious diseases are communicable from person to person, and that these diseases are, in fact, continually developed and spread in this very way, is a matter of familiar knowledge. Now, one hundred and eleven thousand people, speaking in round numbers, out of a population of twenty-two millions contained in England and Wales, die of disorders of that class every year. The deaths from all causes in the same population are less than five hundred thousand in the year. Therefore, nearly twenty-three per cent. of the current death-rate is due to a class of influences which at least is capable of being affected by human intelligence dealing with it as a broad question of sanitary regulation and management.

These communicable diseases, to say nothing for the present of other kinds of morbid derangement, are, certainly, all engendered in the blood. They are due to some injurious change brought about in the material, or adjustment, that has been described. The living blood is the seat both of the disorder that is set up in the individual system, or frame, and of the erratic influence which then carries a similar state of disorder to other systems and individuals, and in that living blood must be sought the potential cause of the baneful result. So much at least is now unquestioned by anyone.

It has been shown that the general constitution of the blood is so ordered that the plastic fluid can flow readily through the delicate capillary channels of the frame where the work of nutrition and renovation of the substance of the living organs has to be carried on. The most frequent form of disease to which the human body is amenable is undoubtedly due to such a change in this particular state of the blood as prevents it from flowing in a free and easy way through the minute channels laid down for its conveyance. The plastic material of the blood, instead of generating life-plasm (bioplasm) in the exact proportion and amount in which it is required for the working needs and capacities of the system, generates it in an over-abundant quantity, or in excess; and the colourless blood-corpuscles, instead of being regularly formed, and moving off in an orderly way as they are produced, to be used up in the formation of fresh ranks of red corpuscles, and in the building up of structure in the various recesses of the body, are irregularly formed and agglomerated into unwieldy aggregations of bioplasm, which quickly choke up and plug the finer channels of the circulation,

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