278 CAUSES OF VARIATION 



the muscle and there forming with its substance definite com- 

 pounds, and he believes the accelerating effect of H or OH is 

 due to their catalytic action in facilitating the formation of these 

 compounds. In this connection it is to be remembered that the 

 serum of the body which bathes the muscles is always, in health, 

 strongly saline and slightly alkaline. 



Further experiments clearly showed that the salts of potas- 

 sium and those of calcium, magnesium, strontium, manganese, 

 and cobalt tend strongly to prevent contraction, this being espe- 

 cially true in the case of potassium and calcium, forcing the 

 conclusion that certain definite substances are necessary to con- 

 traction ; that certain others tend to accelerate and still others to 

 retard this characteristic activity of musctilar tissue. 



Artificial parthenogenesis through changes in the surrounding 

 solution. 1 The indefatigable labors of Jacques Loeb upon this 

 subject have not only thrown much light upon the essential 

 features of fecundation, but incidentally they have afforded 

 results of high value in determining the nature and range of 

 external influences upon the characteristic activities of living 

 matter. 2 



It had long been known that many of the eggs of sea 

 urchins, arthropods, and marine worms, even when unfertilized, 

 would, if left for a comparatively long time in sea water, begin 

 to segment, reaching the two- and sometimes the four-celled 

 stage. Loeb, and later Morgan, found "that if the concentra- 

 tion of the sea water be raised sufficiently by the addition of 

 certain salts, a segmentation of the nucleus takes place with- 

 out any segmentation of protoplasm [cytoplasm]. Such eggs, 

 however, when brought back into normal sea water divide into 

 as many cells as there were preformed nuclei." 3 In none of 

 these experiments did the cell division " lead to the formation 

 of a blastula. A heap of cells, at the best about sixty, were 

 formed, and then everything stopped." As in the case of tumors 



1 Loeb, Studies in General Physiology, Part II, pp. 539-691. 



2 These investigations have been published from time to time, especially in the 

 American Journal of Physiology, and later (1905) in book form under the title, 

 Studies in General Physiology. 



* Loeb, Studies in General Physiology, Part II, pp. 540-541. 



