RELATION TO OTHER SCIENCES 125 



of plants, especially since we have learned how great a role parasitism 

 plays in vegetable as well as human pathology. At the head of the 

 parasitic problems of human pathology of the present day stands 

 that of the etiology of tumors; here cancer cells, here cancer para- 

 sites, so sound the battle-cries, and a parasitic new formation in the 

 vegetable kingdom, the club-root of turnip, did not only have to 

 furnish the paradigma of cancers in man and beast, but some inves- 

 tigators have even gone a step farther and see in Plasmodiaphora 

 brassicae, the parasite of club-root, the exciting cause of animal 

 tumors or at least a close relation of such cause. 1 



Very different is the relation of human to animal pathology, 

 not only on account of the closer relation between man and ani- 

 mal, by reason of which a comparison of observations between 

 animals, especially the higher vertebrates, and human pathology 

 is more permissible, but also because the questions to be decided 

 experimentally must be proved in the main on animals. 



Even though a complete agreement between the phenomena of 

 human and animal pathology cannot exist, as the function and con- 

 struction of the animal body and its organs do not entirely agree with 

 |hose of man; even though many diseases which attack man do not 

 occur in animals, still analogies are not wanting and the similiarity 

 is greater the higher the group among the vertebrates to which the 

 animal in question belongs. An especial advantage of compara- 

 tive animal pathology is that the necessary material is not only 

 easier to obtain than the human, but that particularly by volun- 

 tary killing of pathologic animals accurate morphologic investi- 

 gations can be made at any desired stage and on perfectly fresh 

 tissues free from cadaveric changes. Especially valuable conclu- 

 sions can be drawn in those diseases, which are common to man 

 and animals, the zoonoses and the anomalies of formation, the 

 simpler ones as well as the monsters in the narrower sense. 



A somewhat neglected realm of comparative pathology has re- 

 cently attracted the attention of pathologists in more and more 

 increasing degree; namely, tumor formation in the lower animals. 3 

 From their construction we may expect to draw valuable conclu- 

 sions in regard to the pathology of human tumors, not only in the 

 morphologic but also in the genetic direction. One point espe- 

 cially comes into consideration, which also plays an important part 

 in the utilization of animal pathology in other directions, the pos- 

 sibility of purposeful inoculation experiments from animal to ani- 

 mal. 3 



Unfortunately the great value of experimental research for all 



1 Gaylord, Zeitschr. f. Krebsforschung, I, 1903. 

 8 Pick u. Poll, Berlin, Klin. Wochnsechr, 1903, p. 518. 



3 C. O. Fenger, Experim. Untersuch. iiber Krebs bei Miinsen, Abh. f. Bakterio. 

 xxxiv, p. 28, 1903; Borrel, Epithel. infectieuses Ann. de I'Inst. Pasteur, 1903, no. 2. 



