72 LEONELL C. STRONG 



dcntly not in the rat. The result obtained with the transplanted 

 normal tissue was to be expected — it is a matter of common 

 knowledge that secretions from a corpus luteum can incite nor- 

 mal mammary- tissue development. 

 Loeb has concluded that — 



(a) there is a specific affinity of the transplanted tissue for a certain 

 growth substance given off by the ovaries. This affinity is greatest in 

 the case of normal mammary gland tissue and of adenofibroma of the 

 mammary gland; less marked in the carcinoma of the mammary gland 

 and lacking in the ordinary embryonal tissue, (b) A factor injurious to 

 tissue growth operating in pregnancy. This may be either directly 

 injurious substance or a shortage of ordinary foodstuffs due to the 

 growth of the embryo. There are certain facts which suggest the first 

 alternative rather than the latter, (c) Homoiotoxins seem to strengthen 

 the second injurious factor, while their absence seems to favor the first 

 aiding factor, (d) There seems to be variations in the strength of one 

 or several of these variable factors in various species. 



3. Prevalent conceptions concerning peculiarities and characteristics 

 of the tumor cell {derived from investigations on trans- 

 plantable tumors) 



a. Rhythms of growth. Of all the interesting peculiarities 

 that the cancer cell is supposed to be endowed with, that of 

 alternating periods of depression and growth is the most interest- 

 ing. By plotting curves based upon the percentage indications^ 

 as ordinates and the interval elapsed before the tumor reached 

 the inoculating point as abscissae, Bashford, Murray, and Bowen 

 concluded that the transplanted tumor cell underwent cyclical 

 changes of growth activity. It must be remembered, however, 

 that these data have been collected from market mice. The 

 objection has already been offered (Calkins) that if these were 

 real rhythms of activity in the tumor cell, it could only be 

 determined with accuracy by studying the rate of growth in 

 one host only. 



The English investigators referred to maintain that the fluctuat- 

 ing results obtained are due to the varying ability of the cell 

 to adapt itself to the foreign-host tissue. This matter will 



1 By percentage indications was meant the relative number of the mice inocu- 

 lated that grew the tumor mass progressively. 



