THEORIES AND PROBLEMS OF CANCER 113 



has been successful in every case. The recurrences are easily 

 explained through a small portion having been left in the first 

 operation. When a mouse weighs 30 grammes and a tumour 

 has to be dealt with which perhaps is irregular in shape and 

 weighs from 15 to 20 grammes, requiring therefore a consider- 

 able amount of dissection to remove it, it is obvious that some 

 of the tumour cells may have been conveyed to the adjacent 

 tissues and left behind or that some outlying portion may have 

 been missed. Operations in rats have always been successful 

 in the first instance. In any case, as the second operation 

 to remove the remainder has invariably been successful, these 

 graftable secondary tumours must be placed in a category 

 different from that in which primary tumours are included. 



The method of using emulsions instead of pieces of tumour 

 has been adopted by many observers. Bashford 1 and others 

 have emphasised the need of using accurate doses of tumour 

 cells, stating that only thus can certain errors be eliminated. 

 However desirable accuracy of dosage may be, it cannot pos- 

 sibly be gained by using emulsions of cells, as only living cells 

 are effective. Even in a solid piece of tumour, there must be an 

 unknown number of dead and degenerating cells and many 

 must be killed outright and many more injured in the process 

 of preparing an emulsion. As it must be quite impossible to 

 estimate the proportion of living cells in a measured quantity 

 of emulsion even to within 50 or 75 per cent., I do not propose 

 to touch upon any experiments based upon accuracy of dosage 

 and have only referred to the method as being a possible source 

 of error with regard to the so-called metastases from inoculated 

 tumours. 



It is curious that continual contemplation of little else than 

 these transmissible mouse tumours seems frequently to lead to 

 the adoption of methods really untrustworthy and very mislead- 

 ing for which intense accuracy is claimed. This is illustrated 

 by many of the papers dealing with the subject but by nothing 

 more clearly than by the drawings to scale of the outlines of 

 tumours in mice at various stages after inoculation given in the 

 Reports of the Imperial Cancer Research Fund. The accuracy 

 of the drawings in connexion with the accuracy of dosage 

 referred to above constitutes one of the most important factors 



1 " Resistance and Susceptibility to Inoculated Cancer," Bashford, Murray 

 and Haaland, 3rd Scientific Report, Imperial Cancer Research Fund, 1908. 

 8 



