1911. ] | Spontaneous Cancer in Mice. 535 
frequent in the mammary gland of old mice. These changes have been 
entirely overlooked, up to the present, in the mammary gland of this animal. 
Along with the interstitial changes followed by sclerosis, hypertrophic 
changes of the glandular epithelium are frequent. In some cases the 
evidence favours the view that the epithelial changes are intimately con- 
nected with interstitial lesions, in others the connection cannot be definitely 
established. Ina large number of instances the hypertrophic condition of 
the epithelium appears to be the basis on which tumours develop. The 
suggestion is made that the interstitial lesions may play an essential part as 
a mediate cause of the epithelial changes. An explanation of the interstitial 
changes described may be afforded by nematodes which have been found 
living in the interstitial tissue where their embryos are liberated. They are 
capable of causing considerable inflammatory reaction, and many of the 
histological pictures of inflammation and sclerosis, so often found in the 
mamma of old mice, can with great probability be referred to their presence. 
The hypothesis is put forward that the frequent and multicentric inflam- 
mation throughout the subcutaneous interstitial tissue in which the mamma 
is embedded may explain the frequency and the multicentricity of the 
epithelial hypertrophic changes and of the tumours arising on them. Similar 
considerations apply to the tumours of the lung and perhaps also to the 
lymphomatous conditions. 
Numerous experiments have been made in order to define the relative 
parts played by local causes, such as those described above, or by con- 
stitutional anomalies of the animal in the development of cancer, or, in 
other words, to obtain more exact information on the relations obtaining 
between the tumour-cells and the animal in which they arose. The 
observations thus made may be considered under the following heads :— 
(a2) Inoculations into the same mouse in which the tumour originated 
(autologous or autoplastic implantation). 
(6) Inoculations into other spontaneously attacked mice. 
(c) Inoculations into normal mice, young and old. 
