THE CAUSATION OF DISEASE. I 33 



might convey specific influences from certain maternal tissues 

 to corresponding parts in the child, the " gemmules " thrown 

 off from such maternal tissues would, according to this doctrine, 

 show a. tendency, by their inherent attractive power, to attach 

 themselves to corresponding parts in the child, and so influence 

 the development of these parts. But this is obviously sheer 

 speculation. 



The second and sole remaining method by which the foetus 

 may be affected is by pressure. It is well known that all 

 sorts of mutilations may result in this way, and it is needless 

 to enumerate them. Possibly the shape of the child's head 

 may in some degree depend upon the shape of the mother's 

 pelvis,, for the moulding of the head at birth is probably never 

 entirely recovered from; and thus it may happen that the 

 different kinds of presentation permanently influence the shape 

 of the head by moulding it in different ways, so that a head, born 

 for instance by breech, may be permanently different in shape 

 from what it would have been had it been born by vertex. As 

 showing the influence of pressure upon the shape of the head, 

 it may be remembered that some savage tribes alter the shape 

 thereof by pressure between boards ; nevertheless, the compres- 

 sion which they employ extends over a prolonged period, differing 

 very markedly in this respect from the merely temporary pres- 

 sure of birth.* • • 



* It may be remarked here that the shape of the child's head bears a 

 definite relation to that of the female pelvis. This may be seen by examining 

 the pelves and crania of the different races of man. The two have become 

 mutually adapted to one another, and the adaptation has doubtless been 

 largely wrought by natural selection. On the one hand, any variation in the 

 shape of the head which hindered its birth would tend to the destruction of 

 the child. Hence the shape of the pelvis doubtless largely determines that of 

 the child's head", because in a state of nature, at all events, only those heads 

 are born which are properly adapted to the pelvis. On the other hand, if the 

 pelvis does not properly admit of the passage of the child's head, the mother 

 would be more apt' to die, so. that natural selection maintains the proper 

 adaptation of the pelvis to the shape of the head ; wherefore the shape of 

 the foetal head likewise determines that of the maternal pelvis. Now, the 

 main distinction between the male and female pelvis is undoubtedly the 

 width of the pubic arch. Almost all the other differences follow from it, 

 as . I have proved to myself on a soft artificial pelvis ; for if the tuber ischii 

 be pulled outwards, the arch widens, the symphysis and the pelvic cavity 

 become shallower, the thyroid foramina triangular, and the transverse 



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