I70 BIOLOGY OF THE LABORATORY MOUSE 



operation and unless complete removal is effected recurrence takes place, 

 often accompanied by an increase in rate of growth. 



As long as neoplasms are in contact with serum they acquire an inde- 

 pendence of growth. Spread, or metastasis, through serum is the greatest 

 danger to the life of the host and one of the chief factors of malignancy. 

 Within the host metastases may be lymphogenous,* hemogenous, implanta- 

 tion or transplantation. New colonies of similar tumor cells are established 

 at a distance from the primary tumor, and these in turn may spread to other 

 locations until a generalized involvement of the entire host organism results. 



Tumor cells are parenchymatous neoplastic cells of connective tissue or 

 epithelial descent. The connective tissue tumors form their own stroma 



Fig. 88. — A spontaneous mammary gland carcinoma (X}^)- 



and blood vessels, while in the epithelial tumors the stroma and blood vessels 

 are from the surrounding tissues, with the result that in the latter tumors the 

 vascular supply is abnormal, atypical and more sinusoidal than in normal 

 tissue. There are no new-formed lymphatics in tumors, and it is generally 

 believed that there are no nervous system attachments (21, 31, 38). 



A mouse frequently appears in excellent health when a tumor is small but 

 grossly detectable. As the tumor increases in size, it places increasing 

 nutritional demands upon the host and at the same time there frequently are 

 metabolic changes due to infiltration of, or pressure upon, vital organs. 

 This is accompanied by degenerative changes in the tumor resulting from the 

 faulty blood supply, so that parts of the tumor become necrotic and their 

 waste products find their way into the blood stream. The mouse will 

 develop progressive signs of general ill health with loss of weight and evi- 

 dence of malnutrition, until in the late stages there is a rufiling of the hair, 

 weakness, lowered body temperature and a tendency to kyphosis which gives 



* Rare in mice for lymphatics are so small and delicate that they are easily occluded 



(44). 



