584 PROFESSOli MAKCUS HARTOG. 



proceeds until they become restiiig-cells (iucludiug the 

 enormous oocyte of the bird), which, when once they cease 

 growing and commence to divide, go on doing so till a brood 

 of small cells is evolved, numerous in proportion to the bulk 

 of the original mother-cell ? To find solutions for these 

 problems I made, in the year 1896, a series of preliminary 

 experiments on the developing eggs of the frog and on the 

 extra-vascular blastoderm of the chick ; and announced 

 at the Meeting of the British Association of that 3'ear 

 that both contained, a peptonising ferment, active only 

 in presence of dilute acids. The following year and. the 

 year after I tried, in vain to confirm these results. I 

 was at a loss to understand, these failures till I realised 

 the exceedingly perishable character of such ferments, 

 as pointed out by Keynolds Green. I had, indeed, in the 

 second, and third years, kept my tubes in a dark corner, but 

 1 had followed the routine of coagulating my material with 

 absolute alcohol, drying, extracting with glycerine, precipi- 

 tating with alcohol, and working with the precipitate, again 

 dried and re-dissolved. My first year 1 was able to carry 

 out these processes with but little delay, thanks to the kind 

 help of Mr. E. J. Butler, then my senior scholar (now, 1903, 

 Cryptogamist to the Indian Government) ; but during the 

 attempts to repeat these observations I was pressed with the 

 routine duties of my chair, and allowed the operations to be 

 protracted over a considerable time ; and to this delay 1 

 have reason to attribute the successive failures. This year, 

 1900, i have confirmed my results of 189t3. 



The frogs^ eggs were taken at a time when the segmentation 

 had advanced so far that the white megameres only showed 

 at the blastopores as a small '^ yolk-plug." They were 

 obtained at first by repeatedly cutting in all directions 

 through the albuminous investment with large sharp scissors, 

 and picking out the eggs singly with a lifter, a laborious and 

 tedious task in which i received much kindly help from some 

 of my students. This year 1 found a readier method, that of 

 passing the spawn two or three times through an American 



