SECT. 3] AND EIGHTEENTH CENTURIES 227 



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



Substance or liquid 



investigated Composition Investigator Date 



riate of soda and sulphuric alkali 

 28 grains, jelly, phosphate of lime, 

 and oxyde of iron 2 grains, water 

 242 grains 



Egg (fish, Cyprinus barbiis) Contains a substance dangerous for Crevelt — 



man, the nature of which is unknown 



Egg (insect, Locusta viridissima, and migratoris) 



Shell An animal combustible substance John — 



and phosphate of lime 



Contents Albuminous matter, a yellow fluid John — 



fatty oil, a little jelly and a charac- 

 teristic substance, acid, phosphates, 

 and sulphuric alkali 



The most interesting of the investigators in this table is Dzondi, 

 whose work in 1806 was the first in which definite chemical charac- 

 teristics were systematically followed throughout embryonic develop- 

 ment. It is surprising that so long a time should have elapsed between 

 Walter Needham and John Dzondi: no less than 139 years. 



After 1 8 14 events were to move so rapidly in the world of science 

 that it would not be possible to follow all the embryological work 

 that was done, and at the same time maintain the proper proportion 

 between the historical part of this book and the other parts. The 

 eighteenth century was the period during which the chemical side 

 of embryology began to differentiate and split itself off from the rest. 

 After 1 8 14 it pursued a course of its own, the individual tracks of 

 which I shall mention under their appropriate heads. But another 

 century had yet to pass before the value of the physico-chemical 

 approach to embryology could become generally recognised, and we 

 are ourselves only at the very beginning of this new period. 



A certain contrast may appear between the critical treatment 

 which I have given to the investigators whose work I have been 

 discussing, and the saying of William Harvey's — "all did well", 

 which stands prefixed to this Part of the book. Yet history without 

 criticism is a contradiction in terms, and the praise and dispraise, 

 which I have tried to allot as accurately and justly as I could, is, 

 as it were, technical, rather than spiritual. All the workers who have 

 been mentioned, and others besides them who left no special marks 

 on their time, are worthy of our respect and of our fullest praise, 

 for they preferred wisdom before riches and, according to their 

 several abilities and generations, diligently sought out truth. 



15-3 



