II. Lead in work with the vocabulary types of tumours

The Nature of Tumours. If, up to the present time, our concept of the nature of tumours is still problematical in many ways, it is the more surprising that tumours with their irresistable urge to grow, were already regarded as something peculiar by the physicians of ancient civilizations. "Cancer" was mentioned about 3500 years ago in the ancient Egyptian Ebers papyrus. In the era of Greek medicine it was regarded as an unnatural growth caused by black bile, and was called "carcinoma". This theory remained acceptable for more than thousand years. More intelligent interpretations and discoveries did not begin to appear until medical schools and universities were founded at the end of the Middle Ages, when postmortem findings were given more attention, and the microscope constructed about 1590 gradually made it possible to recognize the structure of tumours. The further development of the science of tumours (oncology) leads, through Morgagni, the founder of modern morbid anatomy (1761), to the related theories of John Hunter, Bichat and Zaennec at the turn of the 18th to 19th century. The tumour was then regarded as a product of the activity of the body, which provided for its nutrition and growth, and with which its structure was comparable. Finally, the histopathological view of tumour structure put forward by Johannes Muller (1838) and Rudolf Virchov (1863) forms the logical preliminary conclusion of the process of discovery.

Definition of Tumours. In modern oncology a tumour is defined as pathological growth lacking the systematic integration in the body which is characteristic of physiological growth. The tumour differs from any other proliferation of tissue in its excessive growth, which persists after extinction of the stimulus which provoked it.

The Genesis of Tumours. The causal and formal genesis of tumours (neoplasms, blastomas) has been the subject of many theoretical interpretations, and still gives rise to lively discussion. The mutation theory of К. H. Bauer synthesizes all the knowledge acquired hitherto and the classical theories in the assumption of a mutational change (due to a hereditary spot) in the cellular property of a tissue in the body, which shows itself in the new "race" of tumour cells, with corresponding biological peculiarities. This chromosomal theory is opposed by the supporters of the cytoplasmic hypothesis, who attribute the peculiar biology of the tumour cell to a change in the cytoplasm (due to carcinogens, oxygen deficiency, etc.). Perhaps both theories contain a grain of truth, and should be applied alternatively or together in different tumours. A neoplastic germ first develops from normal cells, in which neoplastic growth occurs only after the action of further (similar or dissimilar) stimuli.

In an elementary way, a tumour may be set down as the product of a reaction to stimuli which alter cellular metabolism, the "neoplastic reaction" differing from the "inflammatory" reaction mainly by its irreversibility.

The Aetiology of Tumours. A number of tumour-producing causes have been analysed empirically, some of which also reveal their character in animal experiments.They sometimes cause benign and sometimes malignant neoplasms, the latter, in some cases, arising secon-darily on the soil of a benign tumour.

Among the chemical substances, tar products are Known to be tumorigenic or carcinogenic. This discovery dates back as far as 1975, when Pott attributed the scrotal cancer of English chimney-sweepers to the products of coal combustion (soot). After further observations in workers with brown coal or tar or in paraffin factories had produced similar experiences, the experimentally reproduced tar cancer of the skin in mice and other laboratory animals proved the correctness of the relationship. In actual fact, it is the aromatic hydro­carbons contained in tar which are carcinogenic

The inhalation of aniline vapour may," after a latent period of many years, cause benign and malignant tumours of the bladder. On the foundation of the arsenic eczema of vineyard workers (caused by sprays against vineyard pests) carcinomas develop on the palms and soles. Chromate and asbestos dusts have been blamed for the development of lung cancer.

Pathogenic microorganisms, especially parasites and viruses constitute a second group of causes of cancer. They prove carctnogenic chiefly in areas of chronic inflammation, partly caused by themselves. In this class are, among others, certain nematodes with which Fibiger (1913) fed rats and produced cancer of the forestomach, also liver flukes and coast flukes, which may cause cancer of the biliary ducts in man. In the tropics, schistosomiasis causes cancer of the bladder. Tumours caused by viruses include warts in children, some papillomas (e. g. in the larynx) and condylomas, and several tumours of animals. Recent investigations have shown that the virus in many tumours is a secondary product of a neoplasm produced by some other cause.

A contrary opinion is that the virus theory should be applied to all tumours.

Occasionally a mechanical cause of tumours seems probable or admissible, provided that the injury is repeated or chronic. For instance, Indian draught bullocks not infrequently develop cancer of the horn subjected to the one sided strain of the rope. Trauma or accidents and any injuries caused by them appear from experience to be accepted as causes of cancer only in extremely rare cases. In 3.7 million gunshot injuries Dietrich found only 40 malignant tumours near the site of the wound.

Cancer of actinic origin (from electro-magnetic radiations) is due, according to Bauer, to the absorption of energies which cause changes in living tissue in the sense of the mutation theory. Besides the (infrared) heat waves, tissue injuries caused by indirect contact with hot substances chiefly come into consideration. The occurrance of malignant tumours in inguinal testicles can be explained by the "overheated" environment Ultraviolet rays play an important part in the production of "light cancer" in seamen and countrymen. The carcinogenic action of Roentgen and radium rays, to which physicians and research workers were particularly exposed in the early days of radiology, is sufficiently well known.

Some carcinogenic substances or factors are only "conditionally carcinogenic", that is, they do not, by themselves, muse tumours, but they may produce true tumours in con­junction with other causal factors. This complex combination of irritants and conditions is indicated in the concept of syncarcinogenesis.

Spontaneous tumours, especially cancer, can occur, in principle, in both domestic and wild animals, down to insects. Some animal tumours have proved to be transplantable or inoculable, and have been cultivated in tumour research laboratories for decades.

The imperative need to characterize tumours as benign or malignant is a justifiable requirement in medical practice. In spite of all advances this need cannot yet be satisfied by any exact, scientific method, and we have to resort to an empirical biological assessment of the type of tumour

Types of benign liver tumors.

The three most common types of benign liver tumors are called:

1) Memangioma

2) Focal nodular hyperplasia

3) Hepatocellular adenoma