StudH'S on Crown Gall of Plants 457 



ning " the cause of cancer to be " a microbe or protozoon or, in 

 other words, an organism of very small size in comparison with 

 the cell that it was supposed to infect."' He says, 



Tlic possibility of a lari^cr parasite, belongint; to a liit;hcr species, was 

 never seriously taken into consideration and it is not surprising, therefore, 

 that Borrel's first communication on a sarcoma in the wall of a parasitic 

 cyst of the rat's liver should have fallen Hat. But no neglect could dampen 

 his ardor, and with all his characteristic enthusiasm he threw himself into 

 a search for parasites in tumors. Other rat sarcomas were discovered, 

 identical with the first and all in the walls of cysts enclosing a Cysticercus 

 fiisciolaris, the lar\al form of a cat tapeworm. Taenia crassicollis. Acarids, 

 or mites, were found^in the milk ducts about mammary cancers in mice 

 and another, Deiuodex jolliculorum, a common inhabitant of the hair 

 follicles and sebaceous glands, around, or even within, cancers of the skin 

 in man. 



For Borrel there was now no shadow of doubt whatever ; to him the 

 intervention of a parasite was obvious, though he did not assign it a direct 

 role in causation. Cancer being due to a virus, an opinion that Borrel never 

 relinquished, the parasite must act merely as its inoculator. Chance bearer 

 of a carcinogenic virus, threading its way through the tissues, it infects in 

 its progress whatever cells happen to lie in its path. 



This brilliant hypothesis had the misfortune to be announced at a time 

 when it still lacked any scientific foundation and the idea of a carcinogenic 

 virus seemed the purest fantasy, for although it was supported by an 

 observation or two here and there these could easily be explained away as 

 coincidences ; no experimental demonstration had yet been provided. Then, 

 too, the role of Demodex in cancer of the skin seemed more than prob- 

 lematical, for the parasite occurred with equal frequency in cancers and in 

 normal skin. 



Discredited from the first by this medley of findings, true enough, to be 

 sure, but unverified, and by more than questionable inferences, the para- 

 sitic hypothesis had httle to commend it. It fell into complete obhvion, 

 therefore, from which it could be rescued only by such dramatic testimony 

 as that of Fibiger. 



In 1913 Professor Johannes Fibiger, pathological anatomist 

 and director of the Universitetets patologisk-anatomiske Institut of 

 Copenhagen, after years of unwearied research, was to announce 

 that by feeding nematode-infested cock-roaches to rats he had 

 secured several cases of cancer,®" at least changes in the stomachs 

 of rats which appeared to be " true cancerous growths." The 

 nematodes had been taken from muscles of a cock-roach: and the 



*° See a statement in English by Fibiger concerning his early work in Smith's 

 address, Twentieth century advances in cancer research, op. cit., 303-305. Quota- 

 tions of this paragraph from this. 



