III. 8 CHEMICAL COMPOSITION 135 



many of these solutions (cane-sugar, NaCl, Lid, MgCl 2 , 

 MgSO 4 ), have been noticed by many observers (Roux, Hertwig, 

 Morgan, Bataillon). All the more violent solutions attack the 

 yolk-granules. In some cases the effect produced appears to be 

 specific ; thus in lithium salts the ectoderm is often pitted and 

 wrinkled before any degeneration appears in the nervous system, 

 and in ammonia salts, which are highly poisonous, the nuclei 

 are much enlarged, lobed, highly chromatic, and homogeneous. 

 The very similar appearance of the nuclei (Fig. 64) in those 

 stronger solutions of urea which arrest development in an 

 early stage suggests that the ammonia set free is the toxic 

 agent in this case. In solution isotonic with -625 % NaCl urea 

 permits of normal development up to a certain point, when the 

 embiyos die. 



In this connexion it is interesting to notice that Moore has 

 found that sodium sulphate will act as an antidote to the 

 poisonous effect of sodium chloride on tadpoles. Thus the 



A-t 



average length of life of tadpoles in a - NaCl solution was 



o 



four and a quarter days, but was prolonged to twenty-one days 

 by adding from 4 % to 8 % of Na 2 SO 4 . The poisonousness of 

 sodium chloride, sodium nitrate, calcium nitrate, and magnesium 

 chloride to Fundulus embryos and the value of other salts as 

 antidotes has been shown by Loeb, while Lillie has noted that 

 sodium is fatal but magnesium and calcium beneficial to the 

 ciliary movement of Arenicola larvae, a result first obtained by 

 Loeb for the Plutei of Echinus; the muscular contractions of 

 the larva, on the other hand, are inhibited wholly by magnesium, 

 partly by calcium, while sodium is necessary for their con- 

 tinuance. In an artificial solution which combines the three 

 elements in the proper proportions normal development is 

 possible. The nature of the part played by the ions whether 

 toxic or antitoxic is, however, a very open question. 



Arguing from the fact that the evil effects of such salts as 

 sodium chloride and nitrate may be counteracted by calcium and 

 magnesium salts, Loeb has suggested that toxicity and anti- 

 toxicity are functions of valency, and also of electrical charge, 

 since it is further stated that toxicity increases with the valency 



