NEOPLASTIC ABNORMAL GROWTH 249 



Kappa particles are distributed to the cytoplasm normally in a ratio 

 of I particle/600: 1 000 cu. mm. of cytoplasm. 



It should be noted that Kappa in many ways, however, fulfills the re- 

 quirements of a virus. Sonneborn believes it is not a virus since the fac- 

 tors determining mating types in Paramecia are likewise cytoplasmic, 

 and it is thought doubtful that mating types are determined by virus 

 infections. Clearly, these brilliant experiments deserve extension. It 

 would be most illuminating to have further data on the composition of 

 Kappa, its ability to survive in tissue culture or on chick embryo, and 

 the size of the particles. 



The experiments specified concerning cytoplasmic inheritance are 

 discussed, of course, because of the interest in the "virus" theory of 

 cancer, which concerns to a considerable extent the activity of particles 

 supposed to be cytoplasmic in origin and location. The term "virus" is 

 generally employed to specify an agent entirely foreign to the normal 

 tissue it invades, a view derived from the concept of viruses as modi- 

 fied bacteria. It appears that ample evidence is at hand to prove that 

 autopropagating substances which reside in the cytoplasm of cells partic- 

 ipate, in certain instances, in the control of inherited characteristics. It 

 is not at all clear and seems unlikely that these cytoplasmic agents are 

 always of cytoplasmic origin and not genie, and subject, at least to some 

 extent, to genie control. The work of Sax (113) bears on this point. 

 He showed clearly that gene products essential for growth are able to 

 diffuse between the cytoplasm of attached cells but not between isolated 

 microspores. 



It may be well in this connection to quote Wilson ( 1 14) : "The chro- 

 mosomes are as much concerned in the determination of the so-called 

 preformed or cytoplasmic characters as any others." This conservative 

 view is certainly supported by the most convincing evidence and serves 

 to strengthen our contention that somatic mutation, war-weary though 

 the term may be, is still adequate to explain neoplastic disease without 

 the addition of parasitic, foreign, or infectious agents. 



Mammary Tumor Inciter (Milk Agent) 



One of the most dramatic experimental studies of recent years is the 

 one which has to do with an extrachromosomal factor described by 

 Murray and Little (115) which governs the susceptibility to spontane- 

 ous mammary cancer in mice. This was shown by Bittner (116) to be 

 a factor transmitted to the young by the maternal milk. The data on this 



