534 Dr. M. Haaland. [ Feb, 17, 
These figures show that it is hardly likely that excessive physiological 
demands made upon the mamma determine the development of tumours im 
this organ, but that other factors must be looked for. 
The mamme of a large number of old mice, cancerous and non-cancerous, 
have been examined histologically in serial sections, in order to investigate 
whether changes might be found which could account for the frequency and 
the multicentric origin of the tumours. 
Pathological changes are very frequently met with, both in the interstitial 
tissue and in the epithelium. The former occur either diffusely or strictly 
localised, and are more or less of a chronic inflammatory character; the 
epithelial changes are either hypertrophic or cystic in character. The 
interstitial and epithelial changes are often combined. A generalised or 
circumscribed hypertrophic condition of the mammary epithelium occurs 
frequently. A general hypertrophic condition mostly indicates physiological 
activity following on pregnancy, and has no interest for the present purpose. 
Now and then such hypertrophic changes are found in a mouse which is 
beyond the age when a physiological activity of the mamma is to be 
expected, and when the mouse has been kept isolated for five or six months 
without a male. 
The hypertrophic condition, when circumscribed, has a special interest 
because of the similarity of the lesions to early tumour formations. All 
degrees of the process are found, from a slight increase in the number of the 
normal acini forming one lobe to definite hypertrophic nodules. On the 
other hand, all gradations exist between such hypertrophic nodules and true 
tumours, and it is often impossible to decide between the alternatives of 
a hypertrophic nodule and a commencing tumour. These changes in the 
gland epithelium are generally accompanied by a more cellular connective 
tissue. They are very often multiple, and then occur either in the same 
mamma or in several mamme from the same individual. 
The frequency of interstitial changes—inflammation and selerosis—in the 
mamme of old mice of the laboratory is striking. There is evidence that 
the presence of nematodes in the subcutaneous tissue may be made 
responsible—at least to a large extent—for them. In several cases the 
interstitial changes co-exist with typical nodular hypertrophy of the 
epithelium, and this association suggests that the different pathological 
changes, inflammatory processes, sclerosis and cellularity of the connective 
tissue, and the nodular hypertrophy of the epithelium may be linked 
together, and referred to a common cause, the presence of nematodes in the 
subcutaneous tissue. | 
Thus, pathological changes of an inflammatory character are very 
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