1892.] Experimental Embryology. 373 



system from loss or advent of energy from without, provided 

 these changes are specially determined by this outside energy. 



To determine what external forces might he at play in 

 embryologieal phenomena he had thrust large pins into frog 

 larvae, fastening them to wax under water, in the expectation 

 that any electrical condition of the surface wuuld he changed 

 by the addition of a good conductor. As some of the tad- 

 poles developed normally he inferred the electrical state of tin- 

 surface of the body was not a determining cause in the pro- 

 cesses of growth. In this work he found certain abnormal 

 changes in the surface cells when death took place and subse- 

 quently made use of these as a means of determining the con- 

 dition of cells in early stages where there were no movements. 

 The chief result appears, however, to have been the suggestion 

 of a method afterwards very extensively employed. 



Thus as early as 1882 he thrust needles into frogs' eggs to 

 see if the protoplasm were arranged corresponding to the 

 future differentiations, though recognizing the roughness of 

 such attempts which he likens to the casting of a bomb into a 

 factory, in hopes of drawing conclusions from the resulting 

 changes in productivity, as to the character of damage 

 inflicted. 



On withdrawing the needle point from an egg a mass of 

 black, or black and white yolk exudes at once and may 

 afterwards be increased. This extraovate either remains con- 

 nected with the wound by a narrow stalk or else separates and 

 leaves no discoverable trace of the wounded spot. In extreme 

 cases, one-fourth to one-fifth of the bulk of the egg may be 

 thus lost, yet development may proceed. 



Regarding the effects of wounding we find, in general, a 

 large number of eggs develop normally, though many em- 

 bryos formed are weak and small, but there are many abnor- 

 malities, some of which are like those often met with in eggs 

 not operated upon, while others are rarely if ever found in 

 nature. Operation at different stages produces results as 

 follows : 



Injured before cleavage had begun the eggs developed 

 abnormally in many cases, forming larvae with deformed 



