556 SPECIAL HISTOLOGY. 



168. The red substance of the spleen, the pulp, or parenchyma of 

 the spleen, is a soft reddish substance, which fills up all the interspaces 



of the vascular glands, as Sanders (On the Structure of the Spleen, " Annals of Anatomy 

 and Physiology," 1850) and IvOlliker do, seems to us to mistake accidental for essential 

 characters. 



The results of comparative anatomical examination are strikingly in favor of this view 

 of the matter. 



The Malpighian follicles of Birds and Amphibia have no capsules (Remak, Leydig). In 

 Bombinator igneus, according to Leydig, a white substance, the representative of the Mal- 

 pighian follicles, lies in the middle of the spleen, surrounded by a red cortical pulp, into 

 which it directly passes. 



On the other hand, Coluber nalrix, a Reptile, presents the very opposite characters. Here 

 the red pulp is absent, and the spleen has, as nearly as possible, the structure of an ordinary 

 lymphatic gland, consisting of a fibrous stroma, containing cavities full of indifferent tissue, 

 through which a capillary network, arising from the vessels of the stroma, is distributed 

 (Leydig " Anatomisch-Histologische Untersuchungen fiber Fische und Reptilien," 1853). 



In Fishes the same variation occurs. In Hexanchus there are thick-walled Malpighian 

 corpuscles (Leydig). In other Plagiostomes and many osseous Fish there are no distinct 

 follicles, but the indifferent follicular tissue follows the sheaths of the arteries. 



2. The arrangement of the vessels of the Malpighian follicles. Johannes Miiller, who gave 

 the first good account of the Malpighian follicles of vegetable feeders (Mailer's " Archiv," 

 1834), not only states that the follicles are, what all recent researches have shown them to 

 be the representatives of portions of the sheaths of the arteries, but also that the arterial 

 twigs which supply them " sometimes run beside the Malpighian bodies without giving 

 any branches to them, sometimes pass straight through the corpuscles'' (p. 88). However, he 

 appears to be inclined to the opinion that the arterial twigs pass " not so much through the 

 middle of the corpuscles" as in the thickness of their walls. 



All subsequent writers have affirmed that the arterial twigs pass over the surface and 

 not through the substance of the Malpighian follicles, with the exception of Giinsburg and 

 of Dr. Sanders who states, not in the paper we have cited, but in a subsequent communi- 

 cation to the Edinburgh Physiological Society (Jan. 31st, 1851), that by a peculiar method of 

 preparation, he had observed arterial twigs passing diametrically through the substance of 

 the follicles, " stains of blood also, often in linear arrangement, indicating capillaries, were 

 seen in the interior of the sacculi." With regard to the latter point, it will be observed that, 

 in the text, Professor Kolliker also records a single observation of minute bloodvessels in the 

 Malpighian follicles of the Cat. 



In all the Mammalian spleens we have examined (Man, Sheep, Pig, Cat, Rat), we have 

 observed the passage of arteries through the Malpighian follicles and the existence of a 

 capillary network in them, with the utmost ease; we are, indeed, at a loss to comprehend 

 how it is that previous observers have so generally overlooked facts so patent. The method 

 we have pursued has been merely to make a tolerably fine section, containing a Malpighian 

 follicle, with a sharp knife to spread it out with needles, adding nothing but a little weak 

 syrup, and then, placing a thin glass plate over it, we have examined it with both the simple 

 and the compound microscope. The use of the former is especially to be recommended, 

 because by manipulating the covering plate, the whole follicle may be readily rolled about 

 under the eye, and the clearest evidence thus obtained that the arterioles pass through and 

 not over the surface of, the follicles. Acetic acid should not be used, as it renders the con- 

 tents of the follicle opaque; but the syrup is of great service, as it keeps the coloring matter 

 of the blood in the capillaries and renders them extremely obvious. The walls of the 

 capillaries are exceedingly delicate and often indistinguishable as distinct structures. Both 

 the longitudinal inner coat and the transverse muscular coat of the arterioles are very well 

 developed in Man. 



3. Structure of the " contents" of the Malpighian follicles. We have been unable to find 

 either cavity or fluid in the contents of the Malpighian follicles. So far as we have seen, 

 they are solid bodies their outer portion or " wall" being .constituted as above described ; 



