be made as thin as possible. A drop of serum may also be secured from a suspected lymph-node by means of a hypodermatic needle and aspiration. The cover-glass preparation is then allowed to dry in dust-free air.

Several methods of staining have been successfully employed, but most of them, such as the method of Giemsa, by which the organism was first successfully demonstrated, are long and very complicated. The writers have found the method of Goldhorn by far the most satisfactory. This consists in the use of Goldhorn's preparation of polychrome methylene-blue.'

A small amount of the dye is dropped on the specimen without previous fixation, and after two or four seconds it is poured off and the preparation slowly immersed in water. It is important, in doing this, to prevent the deposition of sediment on the specimen; the slide must hence be introduced into the water in a slanting direction, with the preparation side down; after a second or two the slide may be waved to and fro until it is free from stain, when it should be removed from the water and placed in a slanting position to drain. It is allowed to dry naturally, but it is important that the air of the room be free from dust, or the resulting specimen will be difficult to study.

The organism is a very faintly stained spirillum, characterized by its more or less sharp-pointed ends and by its acute angular flexures or turns. It varies in length from half that of a red corpuscle to as much as 25 microns. When stained in the manner directed, the germ is of a purplish-black color; it can be rendered a deep black by washing the stained specimen for from ten to fifteen seconds in Gram's iodin solution. The specimen is mounted and examined with an oil-immersion lens in the usual manner; a persistent search is often necessary to reveal the presence of the spirillum. Impregnation staining methods employing solutions. of silver nitrate and subsequent exposure to light are now used with great success and supply us with the simplest means for the recognition of the organism. For examination of smear preparations, however, the polychrome dyes have as yet proved most

'The methods for preparing this were detailed in the "Journal of Experimental Medicine," March, 1906; also in less detail in the "N. Y. Post-Graduate," February, 1906.

accurate in our hands, but for section staining the silver nitrate methods are most satisfactory.

Recently, dark field illumination, which requires, however, special and expensive apparatus, makes it possible to easily demonstrate the organism in fresh and unstained specimens. It is also highly probable that the serum reaction of Wassermann and Levaditi will finally largely replace the other methods for the early absolute diagnosis of syphilis.

CHAPTER V

THE KIDNEY: ITS EMBRYOLOGY, ANATOMY, AND

PHYSIOLOGY

EMBRYOLOGY

In the development of the body the kidney is preceded by the formation of two kidney-like structures in the intermediate cell mass, the pronephros and the mesonephros, both of which originate from portions of the Wolffian body. These organs contain glomeruli and tubules, not unlike those subsequently seen in the true kidney, and open into the Wolffian duct. In the male the nephros later becomes atrophied, but persistent remains form the parovarium in the female, and parts of the epididymis in the male.

The anlage for the true kidney, or metanephros, appears during about the seventh week of intra-uterine life. Its mode of development is very similar to that of the Wolffian body, and it is similarly formed, chiefly in the intermediate cell-mass of the mesoderm. The tubules are shaped within this tissue, appearing first as blind sacculations in the formation of which the primitive peritoneum now appears to take no part. One extremity of each tube becomes dilated into a spheric body, into which capillaries grow, thus invaginating the walls of the spherule, and so forming the Malpighian body and the capsule of Bowman. Only the cortical portions of the kidneys are developed from the intermediate cell-mass in this manner. The pelvis, the medulla, and the ureters are formed from protrusions of the posterior extremity of the dilated Wolffian duct; these outgrowths pass toward the intermediate mass, and subsequently the tubules of the cortex unite with those that represent the conducting portions of the urinary passages, which are thus derived from entirely different structures. McMurrich states, however, that the entire renal tubule is derived from this outgrowth of the Wolffian duct, and that the intermediate cell-mass contributes only the supporting tissue and the blood-vessels.

The glomeruli appear at about the eighth week, and in the third month the papillæ are formed (Quain). At about the tenth week the surface of the kidney becomes lobulated. The further development and elaboration proceeds along the lines of simple growth.

b

ANATOMY

The kidneys are two bean-shaped organs, lying in the posterior portion of the abdominal cavity, outside the peritoneum, one being on each side of the spinal column, and on a level with the last dorsal and the upper two or three lumbar vertebræ. Usually the right kidney lies somewhat lower than the left, probably due to the pressure on this a side exerted by the right lobe of the liver, the inferior surface of which frequently presents a depression corresponding to its point of application to the kidney.

b

The kidneys are so arranged in the abdominal cavity that their anterior surfaces are slightly everted, looking forward and outward, their posterior aspects being correspondingly arranged in the contrary planes. The normal kidney has an average size of about four inches in length; two and a half inches in breadth; and one and a quarter to one and a half in thickness (Quain); as a rule, however, the right kidney is somewhat longer and thinner than the left. The average weight is about four and onehalf ounces, but both size and weight vary quite constantly, under normal conditions, with the body weight; thus the largest kidneys are generally seen in the largest bodies. Probably on account of this fairly definite relationship between body weight and the

Fig. 60.-Longitudinal section of human fetus of twenty-six days' gestation, showing the pronephros or earliest anlage of renal tissue. a, Wolffian duct; b, b, developing glomeruli of pronephros; c, neural canal; d, posterior root ganglion. Authors' specimen.

size of the renal organs the average size of the kidney in the female is somewhat smaller than that of the male.

The kidneys lie posterior to the peritoneum; the anterior surfaces are directly covered by this membrane, except in stout subjects, where separation by a deposit of fat over the anterior surface of the kidneys often occurs in marked degree. The other aspects of the kidney are, in well-nourished subjects, embedded

Fig. 61.-Kidney from a human fetus of four months' gestation, indicating the differentiation in development between the cortex and medulla. Authors' specimen.

in a thick layer of adipose and areolar tissue, which serves to retain the organ in place and doubtless acts as a very efficient protective layer or insulator, particularly against sudden chills or trauma.

The surface of the adult human kidney is smooth and of a deepred color. Not infrequently, however, it is seen to be more or less lobulated, simulating the kidneys of the fetus and certain of the lower animals.

Anteriorly, the left kidney region is crossed by the pancreas, and the splenic vessel lies just about at the level of the hilum. Above,