PARTURITION— FUERPERIUM— LACTATION 79 



great, yet it has been much exaggerated ; thus Sterne in 

 " Tristram Shandy " refers to it as equivalent to a weight of 

 470 lb., but modern investigations, by means of a mechanical 

 apparatus (a dynamometer, or rubber bag fitted with a mercurial 

 manometer), indicate that it is very much less — perhaps about 

 30 lb. — but show a wide variation. 



Fig. 55. — Noinial birth. The figures 1 to 5 show the positions of the 

 head during successive stages. (From Galabin's Manual of 

 Midwiferij, J. & A. Churchilh) 



When twins are born the second child is usually expelled 

 within half-an-hour or so after the first, but the interval may 

 be greater. 



There are other modes of presentation than the typical one 

 described above in which the head is expelled first, and there 

 are many variations of these modes. If the head is prevented 

 from coming down in the normal manner, owing possibly to 

 irregularity in the pelvis, some part of the pelvic portion of 



