(2) The cellular element predominates; therefore they grow rapidly.

(3) Possessing no capsule, they infiltrate surrounding tissues.

(4) They infect adjacent lymph glands.

(5) They recur even after complete removal.

(6) They give metastasis; that is, they become disseminated in different organs.

(7) Their presence develops a progressive emaciation.

BENIGN TUMORS.

(1) These in and of themselves do not tend to produce death.

(2) As the cellular element is not liable to predominate, they grow slowly.

(3) They are encapsulated, and when diffuse do not infiltrate surrounding tissues.

(4) They do not infect adjacent lymph glands.

(5) They do not recur after complete removal.

(6) They do not manifest metastasis.

Benign tumors, though harmless, may, by the accident of their location, indirectly produce death. Mere pressure on the brain substance of an otherwise innocent tumor, compression of the blood supply for vital organs, growth in such manner as to cause obstruction in the alimentary tract or pressure upon nerves, may cause death, or, prior to death, so combine the effects of anemia (deficiency of blood), starvation, and pain, with its consequent restlessness, as to produce a veritable cachexia (condition of general ill health).

On the other hand, a malignant tumor in its primary growth may so implicate a vital organ as to destroy life before metastasis can occur or even before cachexia can develop. Thus, to the untrained observer, environment may so operate as to cause these two cla.s.ses of new growths to simulate each other. The boundary lines may seem to overlap. It is here that the microscope, as the court of last appeal, adjudicates positively in the diagnosis between these two clearly marked divisions.

It may almost be a.s.serted that a true cla.s.sification of tumors can not be made until we know more about the cause of them. The arrangement here presented is offered to meet the practical needs of the veterinarian, student, and farmer rather than of the pathologist.

We may roughly divide the tissues of the body into structural and lining tissues. The structural tissues are composed of the tissues of special function and simple connective tissues. The lining or covering tissues, both internal and external, are known as epithelium.

Section A of the table below contains the true tumors or proper neoplasms.

Section B includes the cysts, some of which are true tumors, while others are false ones, but the latter are added because of their gross resemblance to the true and the consequent necessity of considering them at the same time.

TUMORS AND CYSTS.

A.--Tumors.

BENIGN.

I.--_Tumors composed of tissues resembling those of special function._

1. Type of muscle tissue Myoma.

2. Type of nerve tissue Neuroma.

3. Type of vascular tissue Angioma.

4. Type of gland tissue Adenoma.

II.--_Tumors composed of fully developed connective tissue._

1. Type of fibrous tissue Fibroma.

2. Type of adipose, or fat, tissue Lipoma.

3. Type of cartilage tissue Chondroma.

4. Type of osseous, or bone, tissue Osteoma.

5. Type of neuroglia, or nerve, sheath Glioma.

6. Type of mucoid, or mucous, tissue Myxoma.

MALIGNANT.

III.--_Tumors composed of embryonic or immature connective tissues._

1. Type of immature connective tissue Sarcoma.

2. Type of endothelial tissue Endothelioma.

IV.--_Tumors in which epithelial elements predominate._

1. Type of various epithelial cells and a.s.sociated tissues Carcinoma.

B.--CYSTS.

I.--_Cysts which develop in preexisting cavities._

1 Retention cysts.

2 Proliferation cysts.

II.--_Cysts which are of congenital origin and are true tumors._

1 Dermoid cysts.

III.--_Cysts which originate independently as the result of pathological changes and are nontumorous._

1. Cysts formed by the softening and disintegration of lesions Softening cysts.

2. Cysts formed around parasites Parasitic cysts.

3. Cysts formed by an outpouring of blood and lymph into the tissue s.p.a.ces with subsequent encapsulation of the fluid Extravasation cysts.

TERMINOLOGY.--The principle of naming tumors is quite simple. The Greek word "oma" (plural "omata") means tumor. This word "oma" is added to the stem of the word ordinarily used to designate the kind of tissue of which the tumor is composed. Thus a tumor formed after the type of fibrous tissue is a fibroma. The only exception to this is in the naming of the two large cla.s.ses of malignant neoplasms. There the names were formed from the fleshlike appearance of the one and the crablike proliferations of the other--namely, Sarcoma (sarks=flesh), carcinoma (karkinos=crab).

DIAGNOSIS.--In the diagnosis of tumors note is taken of (1) clinical history and (2) examination of the tumor.

(1) _Clinical history._--Circ.u.mstances connected with the origin of the tumor and its rapidity of growth may point to an inflammatory swelling rather than a tumor. The location of the tumor at its commencement is important, as, for instance, in diagnosing between lipoma and carcinoma, the former being more or less movable under the skin, while a carcinoma develops in the skin. While tenderness on pressure may be caused by compression of a sensitive nerve by a tumor or by tumors of the nerve or nerve sheaths, as a rule this symptom is indicative of inflammatory swelling rather than of the existence of a tumor.

(2) _Direct examination of the tumor._--In the application of this diagnosis the trained observer will note color, size, shape, and surface structure, transmission of light, movableness, consistence, resistance, pulsation, and crepitation. Percussion, auscultation, and exploration are also available methods. Finally, microscopic examination of the growing portions of the tumor by a pathologist will be found most satisfactory.

GENERAL TREATMENT OF TUMORS.