THE MICROSCOPE IN PATHOLOGY. 263 



tumors, infiltrations, or numerical hypertrophies, the lat- 

 ter differing from simple hypertrophies, or increased size 

 of the elements of tissues, by increase in the number of 

 the elements, as of the muscular fibres in hypertrophied 

 muscle, etc. 



New formations are in all cases the direct product of 

 pre-existing cellular elements, and their development re- 

 sembles more or less the normal tissues. In other words, 

 every pathological growth has its physiological prototype. 

 If it is similar in structure and development to the tissue 

 from which it originates, or in which it is situated, it is 

 called homologous ; when it differs, heterdogous. 



The elements from which new growths most frequently 

 originate are those of the common connective tissue, with its 

 bloodvessels and lymphatics. This tissue must be distin- 

 guished from formed connective substances, as bone, ten- 

 don, cartilage, etc. Two kinds of cells are found in this 

 tissue, the connective tissue cells, which are stable, and 

 the mobile cells, which are probably wandering leucocytes. 



The first result of the abnormal activity of these cells is 

 to produce a new tissue, embryonic or indifferent tissue, 

 composed of small roundish cells, about 5 oWth of an inch 

 in diameter. This tissue afterwards develops into tissue 

 of permanent growth, resembling the immature connective 

 tissue of the embryo, and like that capable of becoming 

 fibrous tissue, cartilage, bone, etc. 



Next to common connective tissue, the epithelia, surface 

 and glandular, are the elements from which new forma- 

 tions most frequently originate, and such growths gener- 

 ally resemble epithelium. 



From the higher animal tissues, muscle and nerve, new 

 growths are rare, if, indeed, they really occur at all. 

 Beale says "the fully formed anatomical elements of a 

 normal tissue could not give origin to a morbid growth." 



The term malignancy is applied to a property possessed 

 by many tumors of recurring after removal, of infecting 



