480 LESLIE B. AREY 



M/100. Practically no response for nearly two minutes, then closure 

 begins progressively throughout the field, glochidia shutting slowly and 

 evenly. A considerable number of initially closed larvae open after 

 one or two minutes. 



M/250. No closure observed in ten minutes, although glochidia 

 still very responsive to touch. Opening of closed specimen observed 

 as at M/100. 



M/500. No effect in five minutes. 



Picric acid was used chiefly as a representative of these substances 

 bitter to human taste. 



Alkalies 

 KOH: 



N/100. All close immediately. 



N/250. Response slow, many shutting late and with a deliberate 

 contraction. 



N/400. Response delayed for about thirty seconds, perhaps one- 

 half closing during subsequent observation period. 



N/600. Few only respond. 



Alcohols 

 Ethyl: 



8M. All respond immediately. 



4M. All close, but in many the response is deliberate. 



M/2. No effect. 

 Methyl: 



20M. All close at once. 



lOM. A few respond promptly, but most very slowly and gradually. 



3M. No effect. 



It is interesting that the really effective solutions, 8M ethyl and 20M 

 methyl acohol, represent concentrations of 37 and 64 per cent, respec- 

 tively. These are lethal doses. 



Sugars 

 Saccharose: 



4M. All close at once. 



IM. Many become shut, but usually only after a distinct latent 

 period. Most that close do so very gradually, some at an almost imper- 

 ceptible rate. 



M/4. No definite effect in ten minutes. Perhaps some had initiated 

 contraction (compare IM), but if so it had not progressed far. 

 Dextrose: 



2M. No effect for several minutes, then contraction enters with 

 such extreme slowness that it can be easily overlooked. Eventually 

 all close. 



IM. Same as in 2M, but even less rapid. 



A 4M solution of saccharose represents a saturated syrup. Hence 

 the action of the other various chemical substances employed is not 

 significantly osmotic. 



