igisl Casimir Funk 35 1 



be propagated by cell-free filtrates. There seems to be a tendency 

 to regard such tumors as entirely different from the known tumors 

 in mice, rats and men. This may be true f or the tumors in mice and 

 rats, from which there are rarely metastases and which, as a rule, are 

 entirely encapsulated. But we do not know whether very mahgnant 

 human tumors, which are metastatic, can be propagated by means of 

 a cell-free filtrate. On the contrary, the tumors in fowls seem to 

 resemble human rather than any other experimental tumors. 



As to the etiology of avian tumors two possibilities exist at the 

 present time. They are either caused by a " filter-passer," as pointed 

 out by Rous, or they are caused by a very unstable chemical sub- 

 stance, of a nature similar to that of vitamine. At present there is 

 only a faint hope for a demonstration of the existence of such an 

 unstable substance, but the problem was attacked by me, in collabo- 

 ration with my late assistant, Mr. Drummond, in an investigation 

 of the chemical composition of tumor extracts. I am also aware of 

 the fact that no comparison can be made between the composition 

 of the tumor, which consists of connective tissue, and of other tissue. 

 Normal breast muscle of the fowl was taken as a control. At pres- 

 ent I am comparing the chemical composition of spindle-cell sar- 

 coma and osteochondroma, with the hope that new chemical sub- 

 stances can be isolated which will prove to be fragments of the 

 hypothetic active substance. 



I have recently found (i6o) that the blood of tumor- fowls 

 (spindle-cell sarcoma) shows a very marked diminution in total 

 nitrogen; as a rule, about 20-30 percent. This difference is not 

 due to a change in the concentration of the serum, for one gets 

 much less blood from tumor animals. It is surprising that this 

 chemical change occurs a few days after the inoculation of the 

 tumor, at a time when there is not the slightest trace of a tumor. 

 At present I am investigating which fraction of the serum-protein 

 is affected. Whether these chemical changes will throw any light 

 on the etiology of the avian tumors we do not know, but they 

 already constitute a perfect method for the diagnosis of these 

 tumors. In human cases, however, such changes in the protein con- 

 tent of the serum could not be detected. This negative result is 

 very likely due to the fact that the chemical changes in the serum 



