368 JOSEPH HALL BODINE. 



closely similar to those indicated for groups. Readings for the 

 same individual, however, are quite constant for any one day. 

 An explanation for these consistent variations is not at hand. 



It is of some interest to compare the present results with those 

 obtained with colorimetric methods by Glaser (7), for grass- 

 hoppers (Melanoplus differ entialis'}. This author found the range 

 of pH values for the blood of these grasshoppers to be 7.2 to 7.6. 

 In previous experiments (6), using a colorimetric method the 

 average pH for the blood of many species of grasshoppers was 

 found to be 6.8. It seems to the author that the results of Glaser 

 (7) are too high, due doubtless to difficulties in the colorimetric 

 method already indicated above. 



Preliminary experiments on the CO 2 tension of grasshopper 

 blood indicate a rather low value, which seems consistent with an 

 acid pH for the blood and the mechanism of tracheal respiration. 



Grasshopper blood seems to be slightly buffered, since upon 

 dilution no marked changes in pH are detected until a dilution of 

 two to four times is reached. Most of the buffer effects are 

 apparently due to the fairly large amounts of phosphates which 

 the blood contains. In contrast to mammalian blood there 

 seems to be present rather small amounts of carbonates. 



Results for pH values of blood for other insects obtained by 

 means of electrometric methods (Bishop, 2 ; Brecher 3) 6.8, agree 

 rather closely with those obtained in the present work for grass- 

 hopper blood. 



SUMMARY. 



The pH values for the blood of different species of grasshoppers 

 have been determined by a micro-electrometric method. Con- 

 siderable variation exists in the pH values for blood of the same 

 species of animals. No correlations seem to exist between blood 

 pH and age or sex. The range and average pH values for the 

 blood of the different species of grasshoppers examined are as 

 follows: 



Species. Range of pH. Average pH. 



Melanoplus femur rubrum 6.4-6.8 6.73 



Melanoplus differentialis 6.42-6.98 6.68 



Chortophaga viridifasciata 6.43-7.05 6.79 



Romalea microptera 6.4-6.8 6.73 



