312 ELECTRO-PHYSIOLOGY CHAP. 



The reaction of ova, which are already at different stages of 

 segmentation, is also interesting. Both in the ovum divided into 

 two or more cells (Fig. 101), as in the morula stage, and again 

 in the blastula, consisting of many little cells, each single cell 

 of the surface shows " special polarisation " when the whole 

 organism is submitted to current, inasmuch as " the cells lying 

 only on the polar side of the ovum exhibit one polar zone, which 

 is visible externally, while the equator takes up the free surface 

 of the cell lying distal to the pole." Further differentiation into 

 smaller and fewer cells, in older blastuke and the gastrula, will, 

 however, under the same conditions, once more bring about a 

 collective equator between two collective polar zones, since a 

 girdle from the poles to the farthest cells remains unaltered. 

 The special polarisation of single cells in the early stages of 

 segmentation would appear to be " bound up with a property 

 which diminishes with their vitality," inasmuch 

 as each attack which weakens the vital energy 

 of the ovum also prevents the formation of 

 special polar zones, wholly or partially, without, 

 FIG. loi.- "Special i lowever effecting the characteristic " total polar- 



polarisation of an 



ovum in four seg- isation " of the entire cell aggregate. Thus Eoux 

 tT action S rfTt'ro7i" remarked in segmented ova treated with weak 

 alternating cur- carbolic acid, which produced no change of form 



rents. (Roux.) ... . , 



externally, that while special polar zones appeared 

 at the first moment of action of the current, they spread rapidly 

 over the whole surface of the cell directly exposed to the cur- 

 rent, so that on each side " a single polar zone, springing, bow- 

 ever, in the upper hemisphere from rounded cells, appears ; 

 while the " general equator," marked off by two parallel sectors, 

 lies between them. With stronger application of the acid 

 there is no reaction. Similar changes are effected by various 

 temperatures. 



If unsegmented ova, or moruke, are left in water for a short 

 time at 3945 C. the reactions are considerably increased, 

 while longer exposure to heat has an opposite effect the moruke 

 no longer exhibiting special polar zones, but only the two " general 

 polar zones " separated by one equator. These results, along with 

 the further fact, that on cooling the ova the reaction to current 

 is considerably retarded, indicate that we are in presence of a 

 vital phenomenon, of which the further investigation promises 



