GLOCHIDIA^ — FACTORS UNDERLYING ENCYSTMENT 485 



relaxations," as Lefevre and Curtis describe for the forms they 

 studied. On the contrary the blood diffuses very poorly. Those 

 glochidia under its immediate influence usually contract with one 

 vigorous snap; those near by remain unaffected. Unless mixed 

 by hand, the sphere of influence of shed blood is restricted. 



Fish blood is notorious for its rapid coagulation; in fact, it is 

 even difficult to obtain successful smears because of this. When 

 a clean cut is made in a gill filament, the end seals so quickly that 

 the excised portion retains the blood within its vessels. Rapid 

 tissue proliferation further covers the cut end. Such an excised 

 filament, washed or not, introduced among glochidia, causes no 

 closure unless brought in actual tactile contact with the soft parts 

 of the larva. If the filament is now cut across with a needle, and 

 the blood forced out, the glochidia enveloped in the blood mass 

 usually close, but those even very close may not. After a time, 

 if considerable blood has escaped, larvae some distance away 

 may become affected, but this closure is usually tardy and 

 lacks vigor. 



The same authors state (p. 154) that ''it was astonishing to see 

 what a small quantity of the fish's blood was required to produce 

 the reaction." Of course, the real effective factor is not the 

 actual quantity, but the concentration. The following ex- 

 periment on Lampsilis luteola will illustrate the efficiency of blood 

 in causing the closing response: 



Buffalo fish were bled and the blood defibrinated. After proving 

 that the serum is effective alone, the blood was diluted with distilled 

 water and the solutions thus obtained added to glochidia according to 

 the method already described (p. 479.) 



1 serum: 4 H2O. Glochidia close quickly. 



1:8. All shut: some tardily. 



1:16. All close, but most after a latent period. 



1:32. Avery few shut promptly; the remainder after a consider- 

 ablelatent period. 



1:64. All respond after several minutes interval. 



1:132. After about one minute some begin to shut; in five minutes 

 perhaps half have closed. 



This sensitivity is of about the grade shown by the hooked 

 types to KCl alone, but is greater than Lampsilis luteola dis- 



