222 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii 



that has converted the arms of all birds into wings, and their hairs 

 and scales into feathers. In advancing these illustrations, we have 

 used the words of our author, that we may not be suspected either of 

 adding to his sentiments or detracting any thing from them." 



If the latter part of the eighteenth century did not produce the 

 move forward in the morphological direction which might have been 

 expected from the work of Wolff, a remarkable amount of work was 

 accomplished on the chemical side. This mass of work did not spring 

 from any one source, it was not due to a great discovery on the part 

 of one man, but rather it came about that, as the technique of 

 chemistry itself improved, a number of otherwise undistinguished 

 investigators, such as Dehne, Macquer and Bostock, applied physico- 

 chemical methods to the embryo, though it is true that among the 

 names are those of certain great chemists, such as Scheele and 

 Fourcroy. The results of this movement were summarised in the work 

 of J. F.John, whose Chemische Tabellen des Tierreichs appeared in 1814. 

 With this date I propose to bring my historical assessment to an 

 end. The work that was done in physico-chemical embryology 

 after 181 4 will be considered in the appropriate sections dealing 

 with the problems of the present time; for Gobley, as an example, 

 who gave the name to the substance still called vitellin, was working 

 only a dozen years after the date of the publication of John's 

 Tabellen. 



In this translation of the Tables, I have made one alteration only. 

 John groups together a number of data which are contained in von 

 Haller's Elementa Physiologiae, and attributes them to that great man. 

 But actually they were obtained by earlier investigators and only 

 came to John through the medium of Haller and Fourcroy — I have 

 therefore allotted them to their true originators. 



EXCERPTS FROM J. F. JOHN'S CHEMISCHE TABELLEN OF 1814 



Substance or liquid 



investigated Composition 



Amniotic liquid (man) It contains a substance which can be 

 precipitated with tincture of gall, 

 phosphate of lime and muriatic salts 

 „ It is salt 



„ It is sweet 



,, It coagulates on boiling 



