178 BOARD OF AGRICULTURE. 



GROWTH. 



There seems a difference between the force utilized in 

 growth and that utilized in development. It is of a more 

 simple power, on account of more simple requirements. 

 Development appears to be dependent more on the primal or 

 inheritable force than growth, which is derived principally 

 from the forces acquired during life, as from food, etc. The 

 two methods are, however, in large degree interchangeable. 

 The essential element of growth is the reception and adding 

 on of new material, whereby bulk is obtained, or a nutritive 

 repetition. Growth and development are usually coincident. 



As an illustration of growth without a corresponding devel- 

 opment, we have the malformed heart. Among the collec- 

 tions in the museum of the Royal College of Surgeons, writes 

 Paget, one among them presents only a single cavity ; no par- 

 tition has been developed between its auricles or its ventricles ; 

 it is, in respect to its development, like the heart of a foetus 

 in the second month ; but though its development was checked 

 thus early, its growth continued, and it has more than the 

 average size of the hearts of children of the same age. 



In the cell, growth may be manifested in the increase in 

 surface or thickness of the cell membrane, or the cell departs 

 from its primitive globular character in such a manner that the 

 cell membranes only add new substance and extend out two 

 or more points. The membranes may become thickened or 

 changed through an infiltration or deposit of hard substances, 

 which may add bulk, or the cell may also divide and form new 

 cells, and these in turn others, while the part necessarily 

 increases in size through this increase of cells. In this case 

 we may have growth to the part and development to the cells. 

 We see instances of this process in the whole history of foetal 

 and early life. In adult age we may have increase of a part 

 through exercise, which result is usually an indication of 

 health. We may have, moreover, growth and development 

 coexistent in the adult in some cases, which are pathological, 

 as in those cases of hypertrophy in which the enlargement of 

 a part is effected with increase of its natural tissues, with 

 proportional retention of its natural form, and with increase 

 of power. 



