296 TUMORS. 



always unsuccessful save in a very few instances, within the limits of the 

 same animal species, and even here the new growths at the seat of trans- 

 plantation have been usually transitory or of doubtful character. The 

 transferred tumor tissue is usually absorbed as foreign bodies commonly 

 are, and the new tissue growths which have been not infrequently de- 

 scribed are apparently for the most part of inflammatory nature. 



We are forced in all these experiments to recognize subtle physiologi- 

 cal conditions peculiar to even closely related species of animals without 

 which their cells cannot flourish or long exist. Grafts of healthy tissue 

 from individuals of the same species, especially of epithelium, may in- 

 deed, as is well known, grow for a time and form foci of abundant new 

 cell production ; but in such cases the new tissue is strictly subordinated 

 to the physiological requirements of the host and does not assume the 

 characters of an autonomous neoplasm. ' 



The Etiology of Tumors. 



The etiology of tumors is one of the most complex and in many ways 

 difficult subjects in general pathology, and with the limitations which 

 the character of this work imposes we can touch only briefly upon some 

 of its more important aspects, referring to more extended works and to 

 monographs for a vast amount of statistical and experimental data, as 

 well as for the many more or less plausible hypotheses which have been 

 framed in the attempts to comprehend these anomalous manifestations 

 of cell energy. 



General Conditions. We shall first consider some of the general con- 

 ditions which seem to have a bearing upon the occurrence of tumors. 



Age. While it may be said in general that tumors are most frequent 

 in adult and advanced life, it is noteworthy that tumors of the connective- 

 tissue type are apt to develop earlier, while the epithelial tumors are 

 more frequent in the later periods. Thus, in one thousand and sixty- 

 three cases of epithelial tumors analyzed by Gallard, only six occurred 

 in the first ten years of life. The most common situation of tumors dif- 

 fers also in the young and in the old. Thus, in the .earlier vjars, as 

 statistics show, the most frequent seat of tumors is the eyes and their 

 adnexa, the kidneys, bones, and testicles ; whereas in adults and the aged, 

 the stomach, uterus, liver, and mamma are most commonly involved. 



Sex. ^ex is also a significant factor in the development of tumors, 

 especially of those which are malignant. Thus, in general, it may be 

 said that the statistics indicate malignant tumors to be about twicft as 

 frequent in females as in males. This proportion, however, does not hold 



1 The results of experimental transplantation of tumors have been well summarized 

 with bibliography by Menetrier in Bouchard's "Traite de Pathologie generale," vol. 

 iii., Partii., p. 752; also by Sailer, Am. Jour. Med. Sciences, vol. cxx., p. 190, 1900, bibl. 

 See further Nichols, Jour. Boston Soc. Med. Sciences, vol. v., p. 34, 1900. Consult also 

 for the results of the transplantation of embryonal cells in the adult animal's body, 

 Birch-Hirschfeld and Garten, Ziegler's BeitrUge, Bd. xxvi., p. 132, 1899, bibliography; 

 see Loeb, Jour. Med. Research, vol. vi., p. 28; also resume by Loeb, with bibl., Jour. 

 Am. Med. Assn., April llth, 1903; also Futterer, Medicine, March, 1902. 



