246 EVOLUTION AND DISEASE. 
founded, nor is the distinction always made with the — 
accuracy that is essential in order to enable us to draw 
conclusions from statistical tables as to the frequency of 
cancer in comparison with other tumours. 
Another circumstance which has never received full 
attention is the great frequency of cancer in the white 
races of mankind. A careful and extensive inquiry into 
this question is very desirable, for we are grossly igno- 
rant as to the occurrence of cancer among the natives of 
colonies, even of India. 
Again, cancer, using the term in the sense in which 
it is employed throughout this chapter, is rare among 
domesticated mammals, and rarer still among wild 
mammals, even those living in captivity. To take one 
example, cancer of the uterus, which is responsible for 
the death of an appalling number of women every year 
in England, is,.as far as my inquiries have extended 
among veterinarians, as well as from my own observations, 
very rare in domesticated and wild mammals. 
The cause of the extreme frequency of cancer in one 
case, and its absence in another, may be in a measure 
explained by certain peculiarities in structure and gland 
distribution. The question is far too extensive to be 
adequately considered in such a work as this, and 
when I have pushed my investigations further I hope to 
deal with it in a systematic manner. 
Before leaving this subject it will be interesting to 
describe a specimen illustrating the close relation which 
exists between glands and cancer. In the section de- 
voted to supernumerary mamme, I drew attention to the 
relation existing between cutaneous recesses and glan- 
