214 PARASITISM 



(Fig. 86). It is sometimes found inside the cancer cells and very often 

 in the detritus of degenerating centres. The dimensions and general 

 character of this spirochete agree with the one which Lowenthal ('06) 

 described from ulcerating human cancer, dog tumors, and in feces, 

 and which he named Spirocheta microgyrata, because of the minute size 

 of the nodes and abruptness of the turns (Fig. 86, left). The ends of 

 the organism are blunt and rounded and there is no evidence of undu- 

 lating membrane or flagellum (as to the nature of spirocheta flagella, 

 see p. 223). Reproduction is evidently by transverse division, but 

 nothing is known in regard to the life history. Similar but not the 

 same species of spirochetes have been found by Borrel ('05) and by 

 Wenyon ('06) in the blood and tissues of mice, and Tyzzer ('07) has 

 found it in tissues of so-called normal mice. It can hardly be claimed 

 that these spirochetes are the cause of mouse cancer, at least not in 

 the form as ordinarily seen. Gaylord and Clowes have found that 

 they are much reduced in number in the tissues after the material for 

 inoculation had been treated with potassium cyanide, although they 

 reappear later. There is reason to believe that, as with Trypano- 

 soma gambiense, under treatment with atoxyl, the ordinary form of the 

 organism may be lost, and that the poison does not kill, but causes 

 them to encyst. The absence of all evidence of similar organisms in 

 human cancer, however, makes it probable that these mouse spiro- 

 chetes, like Leydenia gemniipara, are only commensals finding here a 

 suitable soil for life and multiplication. On the other hand, the 

 possibility that they are inciting or aggravating agents must not be 

 overlooked. 



The cancer problem or problems, finally, must be regarded as still 

 in the stage of working hypotheses, of which no one points out with 

 unmistakable clearness the path for future research. That the field 

 of parasites thus far has been harrowed in vain is no reason for aban- 

 doning this particular working hj'pothesis, at least not until we know 

 more about the still invisible organisms of yellow fever, or those of 

 foot and mouth disease, or until we know more about the minute forms 

 of the organisms of "fixed virus" of rabies, or the stages which pass 

 the filters in claveMe, molluscum contagiosum, dengue, and similar 

 diseases. 



