422 Mr. Lawson Tait on the 



growth, and how perfectly it is seen in joints. It is the universal direc- 

 tion of growth in plants and shells, and may yet be shown to exist in 

 structures where little suspected. If we accept the doctrine of con- 

 tinuous descent, we can be at no loss to account for the presence of a 

 spiral in the umbilical cord, the most lowly organized structure in the 

 human economy. If we do not accept that doctrine as more than an 

 hypothesis, the spiral growth of the cord may yet be advanced as an 

 argument in favour of its establishment. To this end its history must 

 be carefully worked out, and to this I hope to be able to make a con- 

 tribution in another note. 



Virchow is the only author whom I have found to state that capillaries 

 pass from the structures of the child into the substance of the cord ; but 

 there can be no doubt that he is correct. 



I injected a large and fully developed still-born child with a strong 

 solution of Berlin blue in size, under the pressure of 350 millims. of 

 mercury. Every organ was completely injected and the liver had given 

 way. 



At the foetal attachment of the cord, and running upwards from the 

 line of demarcation, was an arrangement of small capillaries. These 

 were visible all round the attachment of the cord, but at some parts were 

 not more than a millimetre in length, while elsewhere they were 8 or 10 

 millims. They did not seem to form loops, but to run straight out from 

 the dermal ring along the cord and immediately under its surface. 



There were five points at which the exaggeration in length was very 

 marked, three of these corresponding to the region of the vein, and one 

 to each of the arteries (Plate 11. fig. 2). 



It will be seen from this that the nutrition and growth of the cord, 

 supposing them to be in part due to this arrangement of blood-vessels, 

 must be unequal — that is, that one side will grow somewhat more than 

 that opposite. This, of course, is certain to result in a spiral ; and this 

 principle of unequal nutrition I hope to be able to demonstrate in further 

 communications as a great principle in all organic spiral growth. 



A further consideration of the arrangement and function of this 

 plexus is given in another division of this note. 



II. Its Covering. 



The naked-eye appearance of the covering of the umbilical cord needs 

 no minute description here. Like all other serous surfaces, it is smooth 

 and glistening, and it is continuous with the epithelium of the amniotic 

 surface of the placenta ; but a very sharp line of demarcation exists 

 between the epithelial surface of the cord and that of the skin covering 

 the omphalic canal. 



This line, however, is only a naked-eye appearance ; for staining and 

 examination by the microscope show that the layers are continuous. 



I have not seen any difference between the structure of the two 



