i86 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii 



[Processus 113.] The fresh albumen of an egg will putrefy. Sound eggs kept 

 at 70° for some days will become foetid and stink. . . .We have learnt then 

 that this is the nature of the material which will shortly be changed into 

 the structure, form, and all the parts of the animal body. Repose and a 

 certain degree of heat produce that effect in that material. We observe 

 therefore the spontaneous corruption and change of the material, and what 

 is extremely remarkable, if an impregnated egg is warmed in an oven [in 

 hypocaustis] to a heat of 92 degrees it employs these attenuated parts 

 changed by such a heat to nourish, increase, and complete the chick for 

 21 days. But in this chick nothing alkaline, foetid, or putrid is found, 

 hence observe, O doctors [medici] , the remarkable manifestations of nature 

 ^by repose and a certain degree of heat a thick substance becomes thin, 

 a viscous substance becomes liquid, an odourless substance becomes foetid, 

 an insipid substance becomes sour and extremely acrid and bitter to the 

 taste, a soothing substance becomes caustic, a non-alkali becomes alkaline, 

 a latent oil becomes sweet and putrid. Let these results be compared with 

 the observations of Marcellus Malpighius on the incubated egg, and we 

 shall observe things which shall surprise us. I took care to investigate only 

 the albumen of the egg first of all, separating the other parts off where 

 possible, for the albumen alone forms the whole of the material which 

 proceeds to feed [in pabulum] the embryo. The other constituents of the 

 egg only assist in changing the albumen, so that when it is changed, it 

 miay be applied to forming the structure of the chick. 



Boerhaave's treatment of these subjects has only to be compared 

 with that of Joachim Beccher, who wrote in 1 703, to show how 

 thoroughly modern in outlook it is. Beccher's Physica Subterranea 

 contains a whole section devoted to the growth of the embryo, but 

 it is extremely confused and very alchemical in its details. The 

 advance made in the thirty years between Beccher and Boerhaave 

 was immense, but, if the biochemistry of development advanced so 

 fast, its biophysics was not far behind, as is shown by the work of 

 G. E. Hamberger and J. B. Mazin. 



Hamberger's most important contributions, contained in his Physio- 

 logia medica of 1 75 1 , were his quantitative observations on the water- 

 content of the embryo and its growth-rate, in which he had no fore- 

 runners, Hamberger showed "that there are much less solid parts 

 in the foetus than in the adult. The cortical substance of the brain of 

 an embryo loses 8694 parts in 10,000 on drying but in the adult it only 

 loses 8096 and that of the cerebellum from 81 parts is reduced to 12. 

 The maxillary glands of the embryo lose out of 10,000 parts 8469, the 

 liver 8047, the pancreas 7863, the arteries 8278 and even the cartilages 

 lose four-fifths of their weight, decreasing from 10,000 to 8149I ". The 



