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 “issue 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 Miller and 
his pupil Virchow. In 1868 Wilks emphasised how this similarity 
