1 88 2.] Organic Physics. 657 



chemical vigor of its weaker pole. In developing there is a 

 tendency to reproduce a normal copy of one parent in one 

 lateral half of the offspring, and the other parent in the other 

 half. But this tendency is checked by the influence exerted by 

 each pole of the germ upon the other, so that the two halves of 

 the body are forced into close though not into exact accordance. 



Chemical vigor of the molecules must give special nutritive 

 vigor to the tissues arising from them, and it may also yield a 

 tendency to increased cellular coherence, thus doubly aiding the 

 growth vigor of these tissues, while the weaker tissues may be 

 more inclined to bud off free cells from lack of local nutrition. 



It is possible that we. have in this diversity of molecular chem- 

 ical activity in the germ an explanation of the marked physical 

 diversities in the tissues thence arising. But there are many cases 

 of abnormal birth which cannot be ascribed to this cause. These 

 abnormalities are very numerous, and differ widely in degree, but 

 may be all grouped under three classes. In one class there is a 

 deficiency in one or more tissues ; in another class there is an ex- 

 cess ; in a third class the tissues are normal but are displaced. 

 In all these classes the normal type of the body is distinctly de- 

 parted from. 



Surgical records give abundant cases in each of these classes 

 of anomalies. In the first class are deficiencies of every degree, 

 from a very slight lack of tissue to an extreme deficiency. In 

 some cases the limbs are missing, in some the head, in some the 

 brain, in others parts of the viscera. Here a mere trunk appears 

 without head or limbs. In the extreme case a mere shapeless 

 lump of flesh is produced, destitute of any organic differentiation. 

 A frequent case of deficiency is a lack of tissue in the line of 

 junction of the lateral halves of the body. This causes coales- 

 cence of organs. In some cases the eyes coalesce, in some the 

 sides of the nose, in some the jaws, this being sometimes so ex- 

 treme that the ears are united into one. Similar cases of coales- 

 cence occur in the viscera, and in the lower limbs, which unite 

 into one. 



The second class of anomalies, that of excess organs, is equally 

 marked. In a not unusual case an extra finger appears on each 

 hand, often accompanied by an extra toe on each foot. From 

 this simple duplication there are cases leading up to the most ex- 

 treme duplication. Three or four eyes, a double tongue, heart, 



