THE STUDY OF CANCER 3 



venience ; since secondary bacterial infections are inimical to 

 the objects of the experiments, they are carefully avoided. As 

 will be explained below, the transference of cancer differs funda- 

 mentally from the transference of any known infective disease. 



Peyrilhe's experiment may, however, be held to have been 

 positive, in that he had produced artificially what were then 

 regarded as the particular features of the " cancerous virus." 

 The repetition of Peyrilhe's experiment to-day could not be 

 justified as a means of throwing light on the nature of cancer. 

 Peyrilhe was under the influence of Descartes' lymphatic theory, 

 as were his contemporaries Alexander Monro and John Hunter 

 in this country. He was ignorant of the true structure both 

 of cancer and of the healthy tissues, and the "cancerous virus" 

 itself was nothing more than the consequences of the action 

 of the organisms of putrefaction on the tissues. It was not 

 till one hundred years later that Lister's experiments on wound 

 infections demonstrated conclusively that this was so. 



Progress was about to be made along unsuspected lines, 

 and during a century the valuable additions to knowledge of 

 the nature of cancer remained almost entirely descriptive. The 

 developments of normal and pathological anatomy, of histology 

 and of experimental physiology, riveted attention. They yielded, 

 as the end result, criteria of the minute structure and nature of 

 cancer absolutely different from those by which the success of 

 Peyrilhe's experiment had been tested. The "cancerous virus" 

 survived ; but had already acquired a changed and vaguer 

 connotation, when, in 1840, Langenbeck found solid nodules — 

 new formations of tissue — develop in the lungs of animals after 

 inoculating them with cancerous tissue from a human breast. 

 Those nodules were taken to imply that the animals had become 

 infected from human cancer, as the nodules in Villemin's experi- 

 ments (1865) were interpreted — as we now know, correctly — to 

 mean the infection of rabbits by the inoculation of tuberculous 

 matter from the human subject. 



The significance of the many resemblances of cancerous to 

 healthy tissues was still unappreciated. It was long in being fully 

 comprehended. Its importance received occasional emphasis 

 early in England, e.g. by Pott, Abernethy, Wardrop, Astley 

 Cooper, Walshe, Hodgkin, Everard Home, Carswell, Wilks, 

 and others, and was fully recognised by Johannes Muller and 

 his pupil Virchow. In 1868 Wilks emphasised how this similarity 



