VARIOUS HUMAN SARCOMAS 123 



tumour-cells. This difference is associated with another namely, in 

 the alveolar sarcoma the parasites have an intranuclear as well as a 

 cytoplasmic phase, whilst in the periosteal sarcoma they are re- 

 stricted to the cytoplasmic phase. This difference in the distribution 

 of the parasites corresponds with what obtains in vaccinia and 

 variola, as was first clearly pointed out by Calkins. This difference 

 of habit in the parasites may be associated with another of equally 

 great importance one that may serve to explain what has hitherto 

 been a difficulty. 



Cancer and sarcoma have till now been regarded as extensions 

 from one original focus. This may be true in some, even in the 

 majority, of instances, and not true in others. Thus, in the periosteal 

 sarcoma the multiplication of tissue-cells, as evidenced to the 

 unaided vision by the bone-formation at the base of the tumour 

 (Fig. 47; a), and as seen in sections in the marrow-cells under the 

 microscope, may be regarded as a defensive pullulation of cells 

 against the invasion of the parasites. Such a tissue-proliferation 

 would result in a tension of tissue increased out of proportion to 

 that of the surrounding parts, and, combined with an invasion of 

 fresh periosteum by the parasites, would account fully for all the 

 known properties of this form of sarcoma local extension, formation 

 of secondary growths in the lungs and elsewhere. This view may 

 be stated thus : A specialized infection results in the proliferation of 

 a certain tissue, which spreads, both locally, increasing the size of the 

 original tumours, and by offshoots extending either in continuity 

 with the original tumour inside veins and lymphatics, and thus 

 spreading like an internal papilloma; or the tips of the papillary 

 extensions becoming detached pass as emboli to distant organs, 

 where the combined proliferation of parasites and of cells, descended 

 from those of the periosteum originally attacked, produce secondary 

 lesions which resemble the original one in all important details, 

 including the periosteal type of tissue-cell originally infected. 

 Writing for students ten years ago on this subject, I said : 



* If, as according to present knowledge is believed, it is the cells 

 of the sarcoma that constitute the infection, there is an evident 



