INTEODUCTION. 6 



positions, in contrast witli simple predisposing causes 

 which act from without. Among these, hereditary pre- 

 disposition is of great importance. When we consider 

 that the parent transmits to the offspring similarity of 

 external structure, with the specialities of function result- 

 ing therefrom, we shall hardly deny that peculiarities of 

 internal structure are also transmissible. So intimate is 

 the connection between the various parts of the body that 

 each must be affected by the others. Thus, the germ-cell 

 and sperm- cell have special family characters manifested 

 only in the product of their development. The parent 

 and offspring being alike in most structural points, and 

 special structure giving special liability to disease, we can 

 understand how it is that hereditary predisposition to 

 disease of special form occurs in such disorders as tuber- 

 culosis and cancerous diseases. The reverse of predis- 

 position is termed immunity. 



Exciting Causes are the direct producers of disorder; 

 sometimes they are enabled to act deleteriously in spite of 

 the absence of predisposition, but generally they find 

 certain favouring states, so, the cautery always arouses 

 diseased action, but a mild external stimulant may simply 

 arouse the activity of the part to which it is applied; the 

 latter, however, becomes an active promoter of mischief 

 when the part is already in a disordered state. Removal 

 of the cause, of all causes, is the grand principle in treat- 

 ment of disease. Our inability to draw a sharp line of 

 demarcation between health and disease is a direct result 

 of deficiency in our acquaintance with structure and 

 function. We cannot yet tell whether structure exists in 

 the protoplasmic contents of cells ; and when we see that 

 a white blood-corpuscle is capable of exhibiting all the 

 properties of life, we cannot doubt that profound secrets 

 of nature, as carried on in the laboratory of cell structure, 

 remain yet to be explored. 



Diagnosis of Disease is determination of the seat and 

 nature of a malady. An animal is brought to us " ill,'' 

 as manifested by certain symptoms. These may be 

 general or special. All animals have certain ways of 



