ill-developed fetus within the developed organism—a fetus in fetu. A regular gradation may be traced from distinct teratoid tumors having irregular mingling of tissue-elements, to malformations in which a more or less systematic outgrowth, somewhat approaching double monstrosities, occurs. Of the distinct teratoid tumors the most frequent is the dermoid cyst. Dermoid Cyst. This tumor presents itself as a cystic formation with a connective-tissue membrane and an inner lining resembling the skin. This may present all the elements of the skin, such as stratified epidermis, a papillary layer, and even subcutaneous connective tissue. Hair-follicles and sebaceous glands are frequent, and habitually long, light-colored hairs are found within the contents, and teeth may be found in the lining membrane or free in the contents of the cyst. The cyst is filled with a semifluid, cheesy mass consisting of epithelial cells, fatty matter, and other detritus. Occasionally dermoid cysts may contain nerve-tissue, muscle, or structures resembling intestine. The dermoid cysts vary in size from minute bodies no larger than a pea to huge masses, the latter being most frequent in the ovaries. Among the situations in which dermoids occur the ovaries are most common; less frequently they are found in the testicles, in the peritoneum, in the membranes of the brain, about the eye, in the neck, floor of the mouth, and elsewhere. Growth is very slow, and they may remain practically latent through life. The nature of these tumors is usually benign, though carcinomatous change may occur, and in the ovaries cystoma is prone to be associated, and the latter may be malignant. Other Teratoid Tumors. Nodular masses may appear about the head or neck or in various parts of the body, consisting of mingled tissues of various kinds, such as glandular tissues, connective tissues, nerve, muscle, etc. These can be classified as teratoid growths. Sometimes they resemble some definite organ, as in the case of growths appearing at the umbilicus of the new-born and simulating the structure of normal intestine. In the neck there are sometimes seen more or less cystic growths lined with epithelium and having in their walls musclefibers, lymphoid tissue, cartilage, etc. These growths probably spring from remnants of the embryonal branchial clefts. The mixed tumors of the parotid gland (see Sarcoma) are allied to these. Cholesteatoma. This tumor is characterized by glistening, whitish, or pearly bodies composed of concentric layers of cells resem bling epithelium (Fig. 77). Sometimes crystals of cholesterin are found in the center of these bodies, whence the name cholesteatoma. Cholesteatomata are found in the membranes or substance of the brain, and present themselves as single or multiple nodules. They are usually soft and glistening in appearance. FIG. 77.-Cholesteatoma from the membranes of the brain. Some authors consider them endotheliomata, but Ziegler has found hair-follicles and hairs in certain specimens, and from this, as well as from the horny change to which the cells in the pearly bodies are prone, classifies them among the teratoid growths. Somewhat similar tumors occur in the pelvis of the kidneys, in the testicles, parotid glands, ovaries, and middle or external ear. CHAPTER VII. BACTERIA AND DISEASES DUE TO BACTERIA. History. Although for many centuries there had existed the idea that disease and decay are due to the action of minute organisms, it was not until the use of the lens enabled the Dutch naturalist Leeuwenhoeck actually to demonstrate their presence in water and in human intestinal contents that the hypothesis of a "contagium vivum" became more than mere guesswork. He discovered, even with his imperfect instruments, short rods, curved and straight, and described their motility. Müller (1785), by the use of the compound microscope, attempted a more systematic classification of these micro-organisms, and from this time many investigators have added much to our knowledge of microbes, that group of organisms which had been denominated by Linnæus by the term Chaos. To the German Henle is due the credit of having first introduced an idea of order into this disorder. He held that fermentation was the result of organic life, and that the action of a contagium was analogous to that of a ferment. The earliest systematic experimental work was that of Pasteur, in which he established beyond doubt this relation between fermentation and the life and development of bacteria. The first definite ideas of the physiology of these micro-organisms are found in his experiments on lactic-acid fermentation, and those of their pathogenesis, in his demonstration of the microbic origin of the silkworm-disease (1869). Davaine and Rayer about the same time established the causal relation of a bacillus found in the blood of a sheep dead of anthrax to that disease. CLASSIFICATION. Bacteria (schizomycetes, or cleft fungi) is the name given to a branch of the lowest and simplest of the orders of the vegetable kingdom. They are small, unicellular organisms, generally free of chlorophyll, and colorless; they possess a cell-membrane albuminoid in composition and homogeneous protoplasmic cell-contents. Some varieties are motile. Nuclei are absent, though in the opinion of some the whole body may be regarded as a nucleus. Bacteria multiply by cell-division, sexual distinctions being absent. In many species resistant forms-spores-occur. The simple elementary forms that occur are of three kinds: the coccus, the bacillus, and the spirillum (Fig. 78). 888 10 K 11 FIG. 78. Various forms of bacteria; 1 and 2, round and oval micrococci: 3, diplococcl; 4, tetracocci, or tetrads; 5, streptococci; 6, bacilli; 7, bacilli in chains, the lower showing spore-formation; 8, bacilli showing spores, forming drumsticks and clostridia; 9 and 10, spirilla; 11, spirochetæ. Coccus. This is a spherical cell, varying in size up to 1 μ in diameter. It takes the anilin-stains readily. Spore-formation and motility are rare. When the cocci are found in groups, the individuals being entirely separate, they are termed staphylococci, from the resemblance of the groups to a bunch of grapes; when in pairs, diplococci; when in chains, streptococci; when in groups of four, tetrads or merismopedia; when in packets, sarcinæ. Bacillus. A rod-shaped, cylindrical cell of varying length and thickness. Spore-formation and motility are common. Most of the group stain easily with the anilin dyes, but some require special methods of staining. Spirillum.-A cylindrical, rod-shaped cell, curved or spiral, sometimes motile. It stains readily. Many other classifications, all of them being to a certain extent artificial, have been made by different authors. Probably one of the most useful and scientific is that of Migula: I. Coccaceæ.-Spherical cells dividing in one, two, or three directions. Endospores rare. 1. Streptococcus.-Division in one direction, the individuals cohering to form chains. Motility absent. 2. Micrococcus.-Division in two directions, the individuals when coherent forming groups of four. Flagella absent. 3. Sarcina.-Division in three directions, forming packets of eight, twenty-seven, or more cells. Motility absent. 4. Planococcus.-Division in two directions, as in the micrococcus. Motility present. 5. Planosarcina.-As the sarcina. Motility present. II. Bacteriaceæ.-Rod-like, cylindrical cells, dividing at right angles to the long axis. 1. Bacterium.-Cells without flagella, often with spores. 2. Bacillus. Cells with peritrichous flagella, often with spores. 3. Pseudomonas.-Cells with polar flagella; spores rare. III. Spirillaceæ.-Cells cylindrical, curved, bent, or spiral. Division as în II. 1. Spirosoma.-Cells rigid, without flagella. 2. Microspira.-Cells rigid, with one, rarely two or three, polar flagella. 3. Spirillum.-Cells rigid, with five to twenty polar flagella. 4. Spirocheta.-Cells flexible, motile, but without flagella: perhaps possessing an undulating membrane. IV. Chlamydobacteriaceæ.-Cells united in a simple unbranched fila- 2. Cladothrix.-Cells united in a filament, with a false branching. 4. Phragmodiothrix.-Cells at first united in an unbranched filament, and dividing in three directions. Later the separate cells break through the thin membrane and grow out as branches. 5. Thiothrix.-Cells united in an unbranched filament contained in a thin membrane. Division in one direction. Cells contain granules of sulphur. V. Beggiatoaceæ.-Cells united in a filament without sheath. Motile, the movement being due to an undulating membrane. MORPHOLOGY. Cell-contents.-The body of the organism in unstained conditions appears as a perfectly homogeneous protoplasmic mass. On staining with anilin dyes a granular appearance is often observed, which under high powers is resolved into a hyaline mass containing numerous chromophilic granules. Vacuolations also are often present. Some modern observers (Bütschli et al.) have made out a network immediately within the membrane and surrounding a central body which readily stains with the nuclear dyes. This latter they regard as a nucleus. Others, however, affirm that this appearance is due to a concentration of the cell-protoplasm (endoplasm), the result of the rather complicated method of staining. The question of the presence or absence of a nucleus is still an open one. In many organisms, as the Bacillus diphtheriæ from a blood-serum culture, for example, there exist certain transparent refractive bodies which stain differently from the rest of the microbe. These metachromatic bodies, as they are called, were regarded by Ernst as nuclear in character. Others look upon them as possibly the primary state of spore-formation. Spore. The spore is a non-vegetative resistant form that the microbe assumes when the conditions for growth are unfavorable. The endoplasm seems to concentrate and become a small, oval, highly refractive body, separated from the bacterial protoplasm by a membrane of its own. It is generally of the same diameter or somewhat smaller than the bacillus itself, and is situated either in the middle (equatorial) or at the end of the microbe (polar spore). It may be larger in diameter than the microbe and cause a swelling at that point. When in the center of the rod this gives rise to the form known as clostridium; when polar, to the so-called drumstick-form (as in the Bacillus tetani). Such intracellular spores or endospores occur among many bacilli. Among the micrococci they are rare; but it is supposed that certain individual cocci become larger and more refractive in appearance and assume the spore-state. These are called arthrospores. Whether these can be regarded as true spores is still doubtful. The spore is extremely resistant to conditions to which the vegetative form readily succumbs; to the action of certain chemical reagents, light, heat, etc. Bacteria that are grown on media poor in nutrient material tend to become asporogenous. A certain temperature is also necessary for spore-formation. Thus, although the anthrax bacillus develops well at a temperature of 14° C. (57° F.), it does not form spores below 18° C. (64° F.). To obligate aërobes oxygen is necessary for their development, and anaërobic cultures present them only in the absence of that gas. Placed under conditions favorable to its vegetation the spore loses its clearness, absorbs water, and swells. A small prominence presents at the side or end, which gradually lengthens and develops into a young bacillus. The membrane of this new microbe is formed from the inner layer of the spore-membrane (endosporium), while the outer layer (exosporium) is cast off. In not all of the varieties of bacilli does sporulation take place, and even where it does occur there may, under certain conditions, as in growth at |