288 PATHOLOGY OF NUTRITION. 



noma e. g., chimney sweeps' cancer, which seems to result 

 from the accumulation of soot upon the scrotum. 



Non-malignant tumors are circumscribed, often encapsu- 

 lated facilitating their complete removal. The absence of 

 capsule in malignant tumors and their extensive infiltration 

 of surrounding tissues make their complete removal impossi- 

 ble, which explains an important clinical characteristic their 

 tendency to recur locally. 



Second, metastasis, or the occurrence of secondary growths 

 in various parts of the body, is but an extension of the ten- 

 dency of malignant tumors to spread locally. Tumor-cells 

 are carried by way of the lymphatics or bloodvessels to 

 distant parts, where they multiply, yet retaining all their 

 original characteristics, such as the tendency to horny degene- 

 ration of the epidermic cells in some varieties of carcinoma. 

 The number of these secondary nodules is often so great as to 

 remind one of the lesions of general miliary tuberculosis. 

 Benign tumors are usually single. 



Third, cachexia: A condition of anaemia, feebleness, and 

 general impairment of nutrition, which is quite comparable to 

 that noted in tuberculosis and other chronic infectious dis- 

 eases, is an evidence of malignancy. 



Fourth, rapid growth. 



Fifth : It may be said that the more cellular a tumor and 

 the less its histological structure follows any given type of 

 tissue i. e. the more atypical the greater the probability of 

 its being malignant. 



Histological classification : Inasmuch as the microscopical 

 study of tumors shows them to be composed of no new tissue- 

 elements, and to conform more or less closely to types of tissue 

 normally present in the body, it is quite natural to classify 

 them according to their microscopic structure. In the study 

 of normal histology we become acquainted with four types of 

 tissue connective, epithelial, muscle, and nervous and with 

 these four varieties correspond four types of tumors. , 



In the connective-tissue group there are the fibroma, composed 

 of fibrous tissue ; the chondroma, of cartilage ; theosteoma, of 

 bone ; the lipoma, of fatty tissue ; the myxoma, of mucoid tissue 

 similar to that of Wharton's jelly of the umbilical cord ; the 

 glioma of neuroglia ; the angeioma of bloodvessels ; and the 



