386 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



growth ceased and a retrogression took place. It is therefore possible to 

 diminish experimentally the growth energy of cancers. These results applied 

 equally to sarcoma of the rat and to adenocarcinoma of the mouse. In some 

 instances a very interesting phenomenon was observed; after heating the 

 tumor in vitro for twenty to twenty-six minutes at 44°C, the growth energy 

 of pieces, after transplantation into a living animal, decreased, but following 

 this early period of slowed growth a certain degree of recovery set in. While 

 usually this recovery was incomplete and the tumors which developed re- 

 mained smaller than is normal for unheated tumors, in some instances the 

 recovery was complete. However, in other cases the growth energy remained 

 weak and at last the resulting tumors became stationary or retrogressed. This 

 was especially noticeable after heating pieces for fifty-five to sixty minutes, 

 when there was a great decrease in growth and recovery was rare. But even 

 under these conditions recovery sometimes occurred and a period of more 

 rapid growth followed. Some tumors showed what we called an oscillating 

 growth, in which a weak growth or a stationary condition, or even an 

 incomplete retrogression, was followed by a definite but slow growth, and 

 this again by a cessation of growth and retrogression. On the whole, the 

 effects of the intensity of heat on the latency period, the growth energy 

 of the tumors, and the number of retrogressions took a parallel course. 



Inasmuch as the change in growth energy of tumors produced by an 

 injurious external agent could persist for a number of cell generations, it 

 became of interest to determine whether repeated applications of heat, in 

 successive transplantations, would lead to a summation of the injurious 

 effects, or whether in the course of subsequent transplantations a recovery 

 might still take place. There was noted such tendency of the tumor cells to 

 recover from these injurious effects and this process seemed to be aided 

 by an intervening transplantation into a new host. However, the restitution 

 of the full growth energy in previously heated tumors was delayed after 

 transplantation under these conditions. There occurs then, after all, in these 

 cases, a summation of injuries caused by the heating and the process of 

 transplantation, but this condition may be followed after some time by 

 recovery. Such a recovery may also take place in tumors which have been 

 injured by other means than heat; a heterotoxin injures the tumor trans- 

 planted into a strange species, but recovery may occur after return into 

 the same species, as Ehrlich has shown. Chambers, Scott and Russ noted the 

 injurious effect of the action of X-rays on rat sarcoma. In this case, also, a 

 gradual recovery was seen after successive transplantations. And inasmuch 

 as the process of transplantation as such is an injurious one, we may con- 

 clude that this faculty to recover from injurious effects is one of the condi- 

 tions that makes possible the continued transplantation into successive gen- 

 erations of strange individuals of the same species. While thus in most 

 instances a summation of the injuries caused by heat, leading to irreversible 

 changes, does not take place in successive generations, but instead recovery 

 follows, the opposite effect, a state of increased resistance to heating as a 

 result of repeated exposures to higher temperatures, is likewise lacking. 



