120 BOVINE PATHOLOGY. 



case of cancer daring its progress and post-mortem, we 

 shall ascertain that the parts diseased are involved in two 

 ways — by primary and secondary disease. The latter 

 changes only are similar to those of special tissues in 

 exanthemata. It seems, too, that as the local elabora- 

 tion and incubation of cancer are remarkably prolonged, 

 so, also, as a rule, its growth in parts secondarily diseased 

 is slow, but from the same cause very potent, and capable 

 of invading all tissues, though some in preference to 

 others, especially those which are actively concerned 

 in cell production. So lymphatic glands and adenoid 

 tissue are most frequently the seat of cancer ; the spleen, 

 liver, and mucous membranes also are liable to this dis- 

 ease. We have not only to deal with circumscribed ac- 

 cumulations of cancer-cells, but also with infiltrations, 

 which in this relation are of the highest importance, for 

 the growth and extension of cancer does not actively 

 irritate sufiiciently to lead to deposits of lymph circum- 

 scribing the diseased parts ; the morbidly active cells 

 have, therefore, free scope for migration, and in whatever 

 situation they become placed can originate changes, for in 

 no part of the body do they materially differ from tissue ele- 

 ments, so uniform has been the development of these gene- 

 ralised cells. Cancerous infiltrations or tumours cause death 

 in two ways, by exhaustion when they are numerous and 

 extensive, and by active interference with the function of 

 a part by disorganisation of its tissues. Prognosis must, 

 therefore, be based upon the position, size, rapidity of 

 spread, and length of existence of the cancer. Injuries 

 of various kinds act as exciting causes, probably by 

 lowering vital actions, and hence power of resisting dis- 

 ease in the part. Hereditary predisposition is very 

 marked, and the diagnosis may be much facilitated by 

 use of the grooved needle and the microscope. In can- 

 cers of hollow organs, as the bladder or the stomach, the 

 characteristic cells may be seen in the contents either 

 after death, or as expelled before. Complications are 

 brought about by the blood taking up morbid material 

 and diffusing it through the system ; by the lymphatics. 



