152 



LIBBIE H. HYMAN 



condition. The desired increase in the value of the ratio 



lowered by placing the pieces in dilute cyanide solutions immedi- 

 ately after section. While this treatment must depress the rate 

 of X also, yet the depression is less than in the case of y, because 

 .r is young, growing tissue, and regulates better to the depressing 



rate of x 

 rate of y 



is thus attained, and as postulated, the percentage of normal 

 heads is decidedly increased. This beautiful experiment was 

 first performed by Child on Planaria dorotocephala, and is readily 

 repeated in the case of Ijumbriculus inconstans. In Table 7 

 are given the results of such an experiment. One hundred short 

 posterior pieces (ab in fig. 23) were cut; fifty were put into water 

 as control and fifty put immediately into cyanide solution of 

 concentration 25;ooo for four days, then removed to water. 



TABLE 7 



As the ah pieces never in my experience yield more than 30 

 per cent of normal heads, the increase here is due to the depres- 

 sing action of the cyanide. 



The converse experiment, that of decreasing the ratio --: ^ — 



* rate of y 



is very difficult to carry out, for it is almost impossible to increase 

 the rate of y, without at the same time increasing the rate of x 

 more. Therefore stimulating conditions, such as increased tem- 

 perature, increased motor activity produce the same effect as 

 in the preceding experiment, as Child has shown; the rate of 

 X is increased more than that of y, and a higher percentage of 

 normal heads results. In Lumbriculus inconstans, however, the 

 desired condition is realized in an unexpected way; in my earliest 

 experiments upon this species I soon found that the 'vitality' of 

 the worms decreases greatly if they are kept for any length of 

 time in the laboratory. The capacity for regeneration diminishes 

 to such an extent that the worms can no longer be used for 



