314 L- V. HEILBRUNN. 



be reversibly prevented by placing them in sea-water concen- 

 trated by evaporation. This concentrated sea-water acted as an 

 anesthetic. Loeb 1 also found that hypertonic solutions made by 

 adding sodium chloride to sea-water prevented segmentation in 

 the sea-urchin egg. The eggs were able to resume division on 

 being transferred to normal sea-water, although the division 

 process was somewhat altered. 



I showed in 1920 as well as in 191 5 2 that hypertonic solutions 

 greatly increase the viscosity of sea-urchin egg cytoplasm. 

 Hypertonic solutions are not the only anesthetics that act in this 

 way. Dilute solutions of potassium cyanide have long been 

 known as anesthetics for sea-urchin eggs. In anesthetic concen- 

 tration, I have shown that cyanide solutions increase proto- 

 plasmic viscosity and render irreversible the normal gelation 

 which occurs in the course of the mitotic process. Chloretone 

 solutions act in a similar way. 



Thus there are two types of anesthesia in the sea-urchin egg. 

 In the one the viscosity of the cytoplasm is decreased, in the 

 other it is increased. The two types of anesthesia differ also in 

 the course of their action on the egg. When the viscosity is de- 

 creased sufficiently, the mitotic spindle is always prevented from 

 forming. Even after the spindle has appeared exposure co ether 

 or to cold causes the astral rays to disappear. On the other hand, 

 anesthetics like hypertonic solutions and cyanide do not have 

 such an effect. As is well known many hypertonic solutions pro- 

 duce asters and spindles. In dilute solutions of cyanide the 

 mitotic process continues until the spindle is formed and then 

 stops. 



Of course in a way both types of anesthesia have one common 

 effect upon the protoplasm. In both cases the protoplasmic vis- 

 cosity is held fixed. Either the protoplasm is kept in a fluid state, 

 or it is made to stay in a stiff condition. The end result is the 

 same. The viscosity changes upon which mitosis depends can 

 not occur, and the egg is anesthetized. 



It is believed that not only in mitosis but in other processes as 

 well, two types of anesthesia occur. This is borne out by a series 



i Loeb, J., /. Morph., 1892, VII., 253. 

 - Loc. cit. 



