tumors in animals.  Under the stimulus of the parasite the cells seem to have unlimited growth capacity and a greater nutritive avidity than have the normal plant cells; the character of the mass produced differs as does the tumor, to a greater or less extent, from the normal growth; on the cedar, for instance, the “witches’ broom” consists of a thick mass of foliage with small stems less green than the usual foliage, the leaves wider and not so closely applied to the stems.  The entire plant suffers in its nutrition and a condition resembling tumor cachexia[1] is produced, and there are no fundamental differences between the plant and animal tumors.  Support has also been given to the parasitic theory by the discovery within tumor cells of bodies which were supposed to be a peculiar sort of parasite.  If the truth of the parasitic theory could be proved, there would be justifiable expectation that the tumor disease might be controlled as are many of the parasitic diseases, but the hypothesis awaits the demonstration of its correctness.  Despite the study of tumors which is being actively pursued in many places and by the most skilled investigators, no parasites have been found in animal tumors; the objects previously described as parasites have been found not to be such.  It is difficult to bring in accord with the parasitic theory the great variation in tumor structure, the relation of certain tumors, as the malignant tumors of the breast and uterus, with the age of the bearer, the congenital tumors which develop in intra-uterine life, and there are many other conditions which oppose the theory.

The traumatic[2] theory.  There is much in favor of this.  In a certain number of cases tumors do develop at the site of injuries.  The coincidence of injury and tumor is apt to be overestimated because of the strong tendency to connect succeeding events.  Tumors are not most common on those parts of the body which are most exposed to injury.  They are rare, for instance, on the hands and feet, and very rarely do they appear at the site of wounds caused by surgical operations.  For those tumors which develop in intra-uterine life it is difficult to assign injury as a cause.  There does, however, seem to be a relation between tumors and injuries of a certain character.  The natives of Cashmere use in winter for purposes of heat a small charcoal stove which they bind on the front of the body; burns often result and tumors not infrequently develop at the site of such burns.  Injuries of tissue which are produced by the X-ray not infrequently result in tumor formation and years may elapse between the receipt of the injury and the development of the tumor.  These X-ray injuries are of a peculiar character, their nature but imperfectly understood, and the injured tissues seem to have lost the capacity for perfect repair.