1910.] Resistance to Implantation of Malignant New Gro wths. 301 



is used to illustrate the facts, since they agree for all the strains that have 

 been tested, whether slowly or rapidly growing. Some tumour-strains illus- 

 trate a larger number of the sum total phenomena than others. Thus, 

 strain " 199 " is very suitable for studying the relations existing between a 

 growing tumour and the host bearing it. This tumour, an adeno-carcinoma 

 of the mamma, has now been propagated for 15 months, and gives from 70 to 

 100 per cent, of tumours when inoculated into a fresh batch of mice. The 

 inoculated tumour-cells proliferate very rapidly, so that, when the strain is 

 in a positive phase of growth, from a dose of 0"05 gramme, tumours weighing 

 about 1"5 grammes may be obtained after 10 days, in all the mice inoculated. 

 The subsequent behaviour of the individual tumours of the same series is 

 very variable ; about a third of them will continue to grow rapidly during tlie 

 next two to three weeks ; another third will show a very much slower speed 

 of growth for two to four weeks, and then resume a speed of growth some- 

 what slower than the original speed of proliferation ; the remaining tumours 

 will be gi'adually absorbed and disappear after 3 to 5 weeks. A single 

 series of daughter tumours of this strain " 199 " illustrates the extremes of 

 behaviour presented by other tumours, viz., those growing progressively and 

 rapidly in all animals inoculated, and those exhibiting transitory proliferation 

 only, even when implantation is successful in 100 per cent, of the animals 

 inoculated. The parts played respectively by active resistance induced con- 

 comitantly with the development of the tumours, and by the qualities of 

 the tumour-cells themselves in determining the different behaviour of different 

 tumours have already been fully discussed (4, 5). 



Advantage may be taken of the behaviour of tumour " 199 " to obtain a 

 concise survey of the nature of the resistance or immunity against the 

 re-inoculation of cancer in animals already bearing tumours. Series of mice, 

 usually 20 in number, bearing growths 10 days old of tumour " 199 " in the 

 right axilla, have been re-inoculated in the left axilla with another tumour 

 either of the same strain or of another strain. Briefly, the result has been 

 that the re-inoculation has failed to give rise to a tumour except in the cases 

 where the tumour primarily inoculated has continued to grow rapidly. 

 AVhere the primarily inoculated tumours have slowed up in their speed of 

 proliferation, or where they have begun to diminish in size, the result of the 

 re-inoculation has been that no tumours developed. In other words, the 

 better the growth of the primary inoculation, the more favourable are 

 the chances for a tumour developing from the second inoculation. This 

 result confirms those previously recorded from this laboratory (5). The 

 possibility can be excluded of the degree of hindrance to secondary inocula- 

 tion being in direct proportion to the rate of growth of the primary ttimour. 



