JoLY — Radio-Therapy : its Scientific Basis and its Teaching. 505 



by thermal radiation of a certain intensity. A method of treatment has even 

 been founded on this. The parallel with the latent image also appears here. 



There is, then, a very complete parallel between the effects of radiative 

 and mechanical stimuli in both cases, the latent image and the cell. The 

 formation of both may be promoted by radiation, and by the same radiation 

 in excess may be finally destroyed. It seems permissible to ask if the same 

 parallel does not extend to more defiuitely chemical effects. The point is 

 important not only on the score of the convenience and accessibility of the 

 plate as a means of investigation, but because of certain conclusions which 

 can be drawn from already known data, and which possibly possess a bearing 

 on what is termed the cancer problem. 



We may state the argument thus : — We find certain chemicals producing 

 in the film what are to all appearance identical effects with those generated 

 in it by radiation. And reasoning from the fact that radiation produces 

 parallel results in the case of the cell and the film, we ask if those chemicals 

 which affect the film in the direction of acceleration or retardation may not 

 also in like manner affect the cell. The view that this question is legitimate 

 is supported by some observational facts, as will presently appear. 



But first it is necessary to look more closely at what may be really involved 

 in comparing the formation of the latent image with the growth of the cell. 

 If, at any stage of its metabolism, a partial (or complete) reducing action 

 takes place in the cell in wliich the halogen and the colloid present take a 

 part, the similarity between the two results may be more than a parallel. 

 It may be based on actions chemically or physically identical, or practically 

 so. There may, in fact, exist, as a stage in the life of the cell, relations 

 between the negative halogen ion, a positive ion united with this, and the 

 protoplasm, similar to that prevailing among the elements of the film. If 

 such exists, the explanation of tlie resemblance in the response of the two 

 systems towards different agents, physical and chemical, is at once forth- 

 coming. We are not in this case involved in the statement that the growth 

 of the cell and of the latent image are parallel actions beyond the inference 

 that a certain molecular rearrangement necessary for the growth of the cell 

 is similar in character to what is presented to our study in the formation of 

 the latent image. In a sense the formation of the latent image is katabolie, 

 that of the cell is anabolic. We are not, however, forcing a complete 

 comparison between them, nor do the observational facts call upon us to do 

 more than recognise some photosensitive molecular process involved in cell- 

 growth similar to one involved in the formation of the latent image. 



There seems to be no doubt that the growth of the cell is highly sensitive 

 towards ionic concentration. Confirming and extending the results obtained 



