GENERAL PATHOLOGY 381 



Deformities. Forster, from whose works the main part of 

 the following chapter is drawn, has classified deformities gener- 

 ally into those involving simple deficiency, stunting or small- 

 ness of the body, and those due to arrested development. All 

 these phenomena, which play so sad a part in the life-history 

 of men, are caused by diseased processes occurring during the 

 early development of the foetus; these processes so disturb 

 the permanent form of the mature individual, that the whole 

 body (or a part of it) becomes misshapen. The causes are 

 hereditary influence, pathological changes in the ovum or 

 spermatozoon, general or local disease of the mother, or ex- 

 ternal mechanical influences. 



The processes of hypertrophy and atrophy, inflammations 

 and hydropic conditions which occur during the inter-uterine 

 life of the foetus can only be recognised by their consequences 

 after it has been expelled from the uterus. 



(a) The worst examples of deformity owing to imperfect 

 development are the formless carneous moles, headless trunks 

 or trunkless heads. Those with imperfectly formed skulls, 

 brains or faces are equally incapable of life, but this is not the 

 case with the microcephalies (produced by premature closing 

 of the bones of the skull), or with those in which the backbone, 

 the thorax or the limbs are imperfectly developed. 



These deformities are possible among wild animals, and 

 the paucity of reported cases is probably due to the fact that 

 the old animals immediately destroy them. 



The teratological preparations in veterinary museums are 

 nearly always from domestic animals. With the exception of 

 microcephaly, the possibility of which among animals I am 

 not at all disposed to doubt, deformities from imperfect de- 

 velopment are fully illustrated by the domestic animals. Much 

 is recorded in the literature of the subject. Darwin ( Variation 

 of Animals) 1 has published a series of striking examples. 

 Thus he mentions a pig which was born without hind-legs, the 

 deformity being transmitted through three generations. In a 

 litter of rabbits one was born with only one ear ; from this 

 a whole race of one-eared rabbits was produced. Exactly 

 analogous to the cases of hereditary baldness among men 



1 Darwin, loc. cit., vols. iii. and iv. 



