PATHOLOGY AND TERATOLOGY. Vll 



strictly ; every day, however, the difficulties of a physio- 

 logical classification will become less, and it may confi- 

 dently be predicted that in a few years this subject will 

 emerge from the darkness in which it has hitherto been 

 involved. 



PATHOLOGY has for its domain the consideration of 

 the abnormal conditions of nutrition which occur in living 

 bodies. Every disease maybe looked upon as an abnormal 

 condition of nutrition, using that term in its widest sense, 

 whether the deviation be structural or apparently only 

 functional. 



TERATOLOGY has for its domain the consideration of 

 abnormal conditions of development. In so far as the 

 function of development is separable from the functions of 

 maintenance and repair, Teratology is separable from Pa- 

 thology ; but there are a large number of intermediate 

 conditions in which it is impossible to distinguish between 

 aberrations of nutrition and of development. Again, there 

 are *various abnormal conditions of growth which may be 

 considered to belong to either class of phenomena. Hence, 

 by common consent, all the diseases peculiar to intra-uterine 

 life, together with certain abnormal congenital conditions 

 of growth, producing dwarfs and giants, have been assigned 

 to the Teratologist. 



As we know that all the functions and parts of the living 

 body are prone to vary within certain limits, so we are 

 justified in believing that the process of development is 

 liable to a certain amount of variation. In some few cases 

 it can be shown that slight variations may occur in differ- 

 ent stages of the developmental process. Thus the occur- 

 rence of transposition, or situs mutatus, of the non-symme- 

 trical viscera is not very unfrequent ; and we owe to Von 

 Baer the following interesting theoretical explanation of its 

 occurrence : 



" The embryo of a bird during the first thirty-six hours 

 lies with its abdominal surface downwards ; but in the 

 course of the third day of incubation in the egg of the 



