Stages of Disease. 97 



economy to sufificicnt number to excite their definite elTects), (c) 

 prodrojiics (a period of indefinite and usually slight symptoms, 

 the first and as yet more or less obscure evidences of the presence 

 of microbes in the system), (d) invasion (the period of develop- 

 ment of tlie specific symptoms of the afifection ; this, if it occur 

 rapidly, is said to be a fnuik iiiiasioii; if gradually, is called an 

 insidious iivz'asioji), (e) acme or fastigium (the period of fullest 

 intensity of the disease), (f) occasionally an amphibolic sta^c (a 

 period of uncertainty and marked variation, corresponding to the 

 popular idea of crisis and used by the author above in this sense), 

 (g) decline (period of disappearance of the disease; this, if it 

 occur rapidly, is said to be "by crisis;" if slowly, "by lysis''), (h) 

 finally, not as a true stage of the disease, but a definite period 

 before health is resumed, convalescence (period of repair and re- 

 building of structures destroyed or impaired in the course of the 

 affection, and of resumption of efficient function by the various 

 parts of the body). If the cause of an acute disease be not a 

 vital one the course includes, of the above stages, only those of 

 invasion, acme, decline and convalescence.] 



However, in such well-known affections, as a result of special 

 etiological factors or the accidental interference of external in- 

 fluences, variations (irregitlarities) may occur, rendering the 

 course an atypical one. In case the symptoms remain for a long 

 time of uniform type and intensity, without appreciable ameliora- 

 tion or increase, the disease is said to be stationary. 



Latent diseases are those which do not manifest themselves, 

 either at all or in part, in certain phases of their development. 

 This depends upon either the impossibility or difficulty of proper 

 examination of the organs, which are the seat of the disease (as 

 the pancreas or some parts of the lung), or upon the fact that the 

 disease is so localizefl or has been so gradual in its development 

 that the function of the organ has not been materially affected. 

 Latency is often, therefore, only a temporary or transient feature, 

 and it is often correct to speak of a latent stage and of a later 

 m.anifested or open stage. Some diseases, even though they be 

 severe, remain latent because they are foUowed by adaptations 

 (compensatory conditions) which entirely prevent their usual 

 symptoms, as when a valvular lesion of the heart is followed by 

 compensatory cardiac hypertrophy. 



When a disease is characterized merely by local symptoms and 

 alterations it is known as a local disease or disease of [this ov 



