930 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The changes produced by quinine and chloral on dividing ova affect 

 the nucleus as well as the protoplasm, and the phenomena of karyokinesis 

 may be seen to be disturbed by these reagents. 



It would seem to be certain that the most important matter is the 

 diminution of the contractile power of the reproductive elements, and this 

 is proved not only by the quiescence of the spermatozoa, but by the stop- 

 page of segmentation and the retrograde metamorphosis which is undergone 

 by the nucleus. 



If the view be correct that quinine and chloral have weakening, and 

 nicotine and strychnine slightly stimulating effects on the contractility of the 

 egg, it is clear that we have fresh means for investigating the significance 

 of the formation of rays in the interior of the ovum. The authors regard 

 the sperm-nucleus and the ends of the segmentation-nucleus as centres of 

 stimuli which have an effect on the protoplasm. It is natural that the 

 homogeneous constituents of the protoplasm, which are the seat of contrac- 

 tility, should stream towards the point of stimulation, and they produce 

 an aggregation of elements ; but it is further probable that the movement 

 should take place in a radial manner, and should thus exercise a directive 

 influence on the passive parts — the granules. But this directive influence 

 can only be exercised so long as the movement which causes it is energetic ; 

 if it is slowed by any agent, the granules would retain their position, 

 and the homogeneous protoplasm would alone be collected around the 

 nucleus. 



Armed by the knowledge of abnormal phenomena which they have 

 acquired, the Drs, Hertwig regard the ray-figures given by Oarnoy as 

 pathological conditions. Increased irritability, weakening, and polyspermy 

 are not the only changes which may be caused in eggs by external in- 

 fluences ; in addition, there are changes in the chemical composition of the 

 substances forming the egg, and that even before the approach of death. 



In dealing with the process of fertilization, it is pointed out that 

 abnormal fertilization may occur when spermatozoa of another species come 

 in contact with the egg, or if many spermatozoa of the same species enter 

 the egg (polyspermy). In inquiring as to the arrangements which prevent 

 abnormal fertilization, the first point of importance is this : no peculiar 

 properties can be observed in the egg which can be regarded as aiding in 

 normal fertilization ; spermatozoa appear to have the tendency to enter any 

 eggs, and in any quantities. Few experiments have been made on this 

 point, but it has been observed that eggs which were sufficiently under the 

 influence of chloroform showed no increased tendency to bastardation. It 

 would, therefore, appear that the chemical bodies which aid fertilization 

 offer no assistance to bastardation. 



Polyspermy can be brought about by chemical, thermal, and mechanical 

 agencies, and the number of spermatozoa increases with the intensity and 

 duration of the agents used; with heating, however, there is a point at 

 which fertilization stops. 



Two hypotheses suggest themselves as explaining how polyspermy is 

 ordinarily prevented ; one is that the fertilizing spermatozoon causes a con- 

 traction of the egg-cell, which prevents the entrance of other spermatozoa : 

 and the other is that the spermatozoon stimulates the ovum to produce a 

 firm membrane — the vitelline — through which other spermatozoa cannot 

 make their way. The former of these may be dismissed now that we know 

 that polyspermy may be aided by reagents which increase the contractility 

 of the egg ; the latter has the support of Fol, and seems to find support 

 from some experiments made by the writers. If ova be placed in sea- 

 water with which chloroform has been shaken up, the membrane appears 



