136 PROTOZOA AND DISEASE 



4. Many of the ' parasitic ' cells are contained within definite 

 capsules (25}. 



5. The end of the process is the destruction of the granulation- 

 tissue cells and the breaking up of the structural basis of the 

 tumour. 



6. The processes described above in the three stages of this 

 tumour occupy the area between the edge and the middle of the 

 section (about vV inch in diameter Fig. 49), whilst in the alveolar 

 sarcoma of the breast the corresponding processes are seen in each 

 capillary mesh, a microscopic area. This difference, as also the 

 greater abundance of tissue-mitoses in the earlier stages of the dog's 

 tumour, is probably associated with a greater rapidity of parasitic 

 invasion in the human sarcoma, and the alveolar character of the 

 latter probably depends upon the same cause. 1 



To repeat, my view is that the course of events in these tumours 

 of dogs may be divided into three stages : 



1. The early granulation-tissue stage i.e., a filling out of the 

 shrunken connective-tissue cells. 



2. A stage in which the granulation-tissue cells have assumed 

 the characters of sarcoma - cells. Some of these cells exhibit a 

 mitotic activity comparable to that seen in the earlier stages of 

 invasion of the cells of the cornea by the protozoa of vaccinia in 

 their hyaline or chromidial phase. Among the tumour-cells in this 

 stage are bodies of typical protozoon characters ; and 



3. A final stage in which chromidial parasites escape from the 

 nuclei of the tumour-cells, rapidly enlarge, become nucleated, and 

 subdivide; this process terminates in the formation of minute 

 bodies, most of which are in the chromidial condition. 



1 In a letter, Brit. Med. Journ., February 2, 1907, I very briefly mentioned the 

 conclusions I had come to as regards the fully developed lesions of this tumour, 

 and in the next issue of the same journal Professor A. E. Mettam wrote to say that 

 he had found spirochsetae among the cells of the lesions, and he kindly sent me, at 

 my request, a preparation in which I saw spiral bodies. Although, from the 

 analogy of syphilis, I think that spiral bodies will probably be found to occur at 

 some stage in the parasite's existence, my experience does not suffice for me to 

 pronounce an opinion as to these particular bodies. 



