182 DISEASES OF CATTLE. 



1, 2, 3.) This shows that both have been derived from the same 

 primitive laj^er of the embryo, which possessed the plastic power of 

 building up a given structure or set of organs. An inclosed ovum, 

 on the other hand, has no such identity or similaritj'^ of structure to 

 the part with which it is connected, showing an evident primary 

 independence of both life and the power of building tissues and 

 organs. The power of determining extra growth along a given 

 natural line is very highly developed in the early embryo and is 

 equally manifest in the mature examples of some of the lower forms 

 of animal life. Thus a newt will grow a new tail when that member 

 has been cut off, and a starfish will develop as many new starfishes 

 as the pieces made by cutting up the original one. This power of 

 growth in the embryo and in the lower form of animals is compa- 

 rable to the branching out again of a tree at the places from which 

 branches have been lopped. The presence of this vegetablelike 

 power of growth in the embryo accounts for most double monsters. 



The influence of disease in modifying growth in the early embryo, 

 increasing, decreasing, distorting, etc., is well illustrated in the 

 experiments of St. Hilaire and Valentine in varnishing, shaking, or 

 otherwise disturbing the connections of eggs and thereby producing 

 monstrosities. One can easily understand how inflammations and 

 other causes of disturbed circulation in the womb, fetal membranes, 

 or fetus would cause similar distortions and variations in the gi'ow- 

 ing offspring. It is doubtless largely in the same way that certain 

 mental disturbances of a very susceptible dam affect the appearance 

 of the progeny. The monstrosities which seriously interfere with 

 calving are mainly such as consist in extra members or head, which 

 can not be admitted into the passages at the same time, where some 

 organ of the body has attained extra size, w^here a blighted ovum 

 has been inclosed in the body of a more perfect one, or where the 

 body or limbs are so contracted or twisted that the calf must enter 

 the passages doubled up. 



Treatment. — Extraction is sometimes possible by straightening the 

 distorted members by the force of traction ; in other cases the muscles 

 or tendons must be cut across on the side to which the body or limbs 

 are bent to allow of such straightening. Thus, the muscles on the 

 concave side of a wry neck or the cords behind the shank bones of a 

 contracted limb may be cut to allow of these parts being brought 

 into the passages, and there will still be wanting the methods de- 

 manded for bringing up missing limbs or head, for which see para- 

 graphs below. In most cases of monstrosity by excess of overgrowth 

 it becomes necessary to cut off the supernumerary or overdeveloped 

 parts, and in this same general principles must be followed as laid 

 down in " Embryotomy " (p. 200). 



