3. From differentiaied cells which, re verting to a simpler, more embryonic type, with this reversion gain the capac ity for active and excessive proliferation. J. G. .Adami (Jacobi Festschrift; Phila. Med. Jour., May 26, 1900).
We can only say that, for the develop ment of a tumor, inherited and acquired characteristics of certain cells and groups of cells show a tendency to increased activity, with the formation of atypical tissue.
Classification of Tumors. — Tumors should be investigated in the same man ner as the botanist studies plants: by groups, genera, species, and varieties. This method of procedure has been best elaborated by J. Bland Sutton, in his work on tumors, innocent and malig nant, and the arrangement herein fol lowed is based largely upon his classifica tion as there given.
According to Sutton, tumors are con veniently arranged into four main groups, each group containing several genera, each genus having one or more species, each species being divisible, in turn, into one or more varieties. The groups and genera are based on their mi croscopical and embryonal appearances, while the species usually represent their situation in the body or some striking characteristic.
The groups are: I. Connective-tissue tumors. II. Epithelial tumors. III. Dermoids. IV. Cysts. Subgroup: pseu docysts.
Lipomata.—Lipomata most frequently grow in those situations where fat is nor mally present, exceptions being found, as in the brain and the submucous tissue of the intestine. They may be single or multiple, and frequently reach a large size, weighing at times as much as 100 pounds. Even in marked emaciation a fatty tumor does not show the atrophy which one would naturally expect. An hereditary tendency is sometimes noticed. Ulceration often takes place at a point opposite the entrance of the blood-ves sels, and pyogenic micro-organisms may gain access to the body by this means. There is often a history of a blow or of irritation to account for the development of these tumors.
Macroscopically, lipomata are com posed of adipose tissue, and appear as rounded, lobulated, capsulated masses. They may be pedunculated. Septa con taining the blood-vessels run from the capsule, dividing the tumor into lobules. They frequently undergo myxomatous degeneration, and show calcareous infil tration. Unless irritation has occurred, lipomata are movable within their cap sule. Care must be taken not to mistake this class of tumors for cysts, especially if they are situated upon the head. The sucking cushions of the cheek in ema ciated children sometimes stand out prominently and may be mistaken for lipomata. Madelung ("Ueber den Fet thals," Langenbeck's Arch., vol. xxxvii, 'SS) has observed in males a rare nodular and infiltrating lipomatous condition in the neck (fatty neck).
On the palm of the hand, where they are usually congenital, they may simulate a ganglion. Lipoma of the palm or in other situations may be distinguished from a fluid collection by spraying ether over the part. In case of lipoma the fatty matter will become solidified by the cool ing process. In a recent post-mortem the writer found that the surgeon had mistaken some small lipomatous masses in the inguinal canal for the omentum, and had reduced the sac of the her nia, believing it to be bowel. Persons have worn trusses for years, thinking that they had hernia, where the masses were only fat. The appendices epi ploicte when markedly enlarged may be considered to be lipomata. Microscop ically the tissue looks like ordinary fatty tissue, but the full-formed cells are rather larger, and numerous smaller connective tissue cells are found, containing, as yet, little or no fat. The cells are frequently polyhedral from pressure.
Chondromata.—Chondromata, or en chondromata, are tumors which are chiefly made up of cartilaginous tissue. Connective tissue usually covers their surface (perichondrium) and forms pene trating bands in which the blood-vessels are to be found. They usually develop in those situations where cartilage is nor mally to be seen, but they also occur in those situations where one normally does not expect to find cartilage, as in the testicle and the parotid. Sutton (Prac titioner, Nov., '97) states that chondro mato are fifty times as frequent in the parotid gland as in the submaxillary. No case has been described in the pancreas. In bones they usually originate in the periosteum and the marrow, though they often spring from remnants of cartilag inous tissue which have not been con verted into bone. In one of my cases the tumor grew from the pelvis, and reached the size of a fcetal head, the cartilage be ing almost as pure as that seen in a joint. The blood-supply, however, was poor. These tumors often appear multiple upon the hands and feet. The variety of cartilage is usually hyaline. Microscop ically some of the cells are capsulated, while others are oval, polyhedral, or spindle-shaped. They are very irregu larly distributed, and assume different forms in the same tumor. Chondromata which develop from previously existing cartilaginous tissue are often spoken of as ecchondroses. The cells undergo fatty degeneration, myxomatous change, calci fication, and ossification. Virchow has described, in the middle line of the clivus in the region of the spheno-occipital articulation, small tumors containing cartilage, which are either found under the dura or break their way through into the arachnoid and pia.