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rently the proof is as plausible as possible. The observer starts with the supposition that pus has found its way into the blood; he examines the blood and really discovers elements, having all the appearance of pus-corpuscles, and in very great numbers. Even if it be admitted that colourless blood-cells may look like pus-corpuscles, still the conclusion which has repeatedly been arrived at in cases of pyæmia, is very seductive, namely, that on account of the great multitude, they cannot possibly be colourless blood-, but must be pus-corpuscles. This was the conclusion arrived at years ago by Bouchut on the occasion of an epidemic of puerperal fever which he then took to be pyæmia, but has very recently, founding his opinion upon the same observations, declared to have been acute leukæmia. It is moreover the same conclusion which Bennett came to in the much-discussed matter of priority between us, when he observed a case of indubitable leukæmia some months before I saw my first case, and inferred from the presence of colourless corpuscles in larger numbers than in any instance upon record, that it was a case of "suppuration of the blood." This conclusion of his indeed was not original, but was based upon the hæmitis of Piorry of which I lately spoke (p. 155), this physician having conceived the blood itself to become inflamed and engender pus, a state which was afterwards denominated spontaneous pyæmia by the Vienna school.

Now all these errors proceeded from the circumstance that such an enormously great number of colourless corpuscles were found in the blood. Now-a-days their occurrence can be just as simply explained according to our theory of hæmatopoiesis, as it previously seemed explicable only according to that of pyæmia. Irritation of the lymphatic glands explains without any difficulty the increase in the colourless, pus-like cells in the blood, and that too in all cases-not only in those where pyæmia was expected

to be found, but also in those where it was not expected, but where the blood notwithstanding exhibited the same quantity of colourless corpuscles as in genuine pyæmia answering to our clinical notions of the disease.

Thus it has been shewn, that every meal produces a certain state of irritation in the mesenteric glands, inasmuch as the constituents of the chyle which are conveyed to these bodies, act as a physiological stimulus to them. The milk which we drink, the fatty matters in our soups, the various kinds of fat distributed in a state of minute division throughout the more solid articles of our food, find their way in the form of extremely minute globules into the lacteals and diffuse themselves there just like the cinnabar in the glands; but the smallest of the fatty molecules after a time force their way through the gland. For such minute bodies therefore there still exists a real permeability in the channels of the gland, but even they are for a time retained, and it always takes a long time before the mesenteric glands after a meal again become entirely free from fat, and the propulsion of this substance through them is manifestly effected by a proportionately strong pressure. At the same time we observe an enlargement of the gland, and likewise after every meal an increase in the number of colourless corpuscles in the blood-a physiological leucocytosis, but no pyæmia.

In proportion as pregnancy advances, as the lymphatic vessels in the uterus dilate, and the interchange of material in the organ increases with the development of the fœtus, the lymphatic glands in the inguinal and lumbar regions become considerably enlarged, and that sometimes to such an extent, that, if we were to find them in a similar state at any other time, we should regard them as inflamed. This enlargement conveys into the blood an increased quantity of fresh particles of a cellular nature, and thus from month to month the number of colourless corpuscles

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augments. At the time of birth we may see in the defibrinated blood of nearly every puerperal woman, whether suffering from pyæmia or not, the colourless corpuscles forming a pus-like sediment. This too is a physiological form which is far from being a pyæmic one. But if care

be taken to select a puerperal woman, offering symptoms of disease which correspond with those usually presented by pyæmia, nothing is easier than to find these numerous colourless multi-nuclear cells, which are precisely such as are supposed to corroborate the presence of pyæmia. These are fallacious conclusions which result from imperfect knowledge of the normal conditions of life and development. As long as we are exclusively bent upon proving the presence of pyæmia, all this may have the appearance of being a great and new occurrence, and we may, when we examine the blood of a woman in child-bed, consider oursider ourselves justified in concluding that she has pyæmia even before its symptoms declare themselves. But we

may examine when we will, we shall always find some traces of leucocytosis, just as it has already long been known that it is very common for a buffy coat to form in the case of pregnant women, because their blood generally has conveyed into it a larger quantity than usual of a more slowly contracting fibrine (hyperinosis). This is accounted for by the increased nutrition of the uterus, and by the changes, so nearly allied to inflammatory processes, which are going on in the uterine system, and are associated with a certain amount of irritation in the lymphatic glands immediately in connection with it.

If we proceed a step farther and consider pathological cases, we meet with these leucocytotic conditions in the whole of that series of diseases which are complicated with glandular irritation, and in which the irritation does not lead to a destruction of the glandular substance. During the progress of an attack of scrofula, in which,

if the disease run a somewhat unfavourable course, the glands are destroyed, either by ulceration, or cheesy thickening, calcification, &c., an increased introduction of corpuscles into the blood can only take place as long as the irritated gland is still in some degree capable of performing its functions, or still continues to exist; as soon however as the gland is withered or destroyed, the formation of lymph-cells likewise ceases and with it the leucocytosis. In all cases, on the other hand, in which a more acute form of disturbance prevails, connected with inflammatory tumefaction of the glands, an increase in the colourless corpuscles always takes place in the blood. So it is in typhoid fever, in which we observe such extensive medullary (markige) swellings of the abdominal glands; so it is in cancer patients, when irritation of the lymphatic glands manifests itself; so, lastly, is it in the course of the processes which come under the denomination of malignant erysipelas and are so early wont to be accompanied by glandular swellings. Such is the meaning of this increase in the colourless elements which ultimately always refers us to an increased development of lymph-corpuscles within the irritated glands.

It is now of importance that I should point out to you, that at present our conceptions concerning lymphatic glands are much more comprehensive than they were a short time ago. The most recent histological investigations have shewn that, in addition to the ordinary well-known lymphatic glands, which are of a certain size, a great number of smaller apparatuses exist in the body which possess precisely the same structure, but do not exhibit such a complex arrangement as we find in a lymphatic gland. To this class belong above all the follicles of the intestines, both the solitary and the Peyerian. A Peyer's patch is nothing more than a lymphatic gland spread out as it were upon the surface; the individual follicles of the patch, just as

the solitary follicles of the digestive tract, correspond to the individual follicles of a lymphatic gland, only that the former, in man at least, are disposed in a single layer, the latter in several. The solitary and Peyerian glands have therefore nothing at all in common with the ordinary glands which pour their secretions into the intestinal canal; on the contrary, they rather hold the position, and manifestly also fulfil the functions, of lymphatic glands.

To the same category belong in all probability also the analogous apparatuses which we find grouped together in such large masses in the upper part of the digestive tract, where they form the tonsils and the follicles of the root of the tongue. Whilst in the intestine the follicles lie spread out on an even surface, in these parts the surface is inverted and the individual follicles lie around the involuted membrane.

To the same category belongs moreover the thymus gland, which in its interior exhibits no other differences of structure excepting that the aggregation of the follicles reaches a still higher degree than in the lymphatic glands. Whilst in most of the lymphatic glands we have a hilus, where there are no follicles, this ceases to be the case in the thymus gland which has no hilus.

Finally to the same class belongs also a very essential constituent of the spleen, namely, the Malpighian or white bodies, which in different persons are distributed in just as different numbers throughout the parenchyma of the spleen, as the solitary and Peyerian follicles in the intestine. In a section through the spleen we see the trabeculæ radiating from the hilus towards the capsule and enclosing certain districts of glandular substance, within which the red spleen pulp lies, interrupted here and there by a sometimes greater, sometimes less, number of white bodies (follicles) of larger or smaller size, single or in groups, and sometimes