A SIMPLE METHOD OF OBSERVING THE AGGLUTINATION OF 

 THE BLOOD CORPUSCLES IN GAMMARUS. By John Tait. 

 (From the Laboratory of Pliysiology, Edinburgh University.) 



{Received for 'publication 12th July 1908.) 



If the antennae of Gammarus marinus are observed with a low power of 

 the microscope the circulation of the blood is readily seen. Gammarus 

 has two pairs of antennae of approximately equal length. The terminal 

 part in each consists of a many -jointed filament which gradually tapers 

 towards the free end ; it is in this filament that the circulation is best 

 seen. The anterior antenna is better suited for observation than the 

 posterior, which is covered with brushes of setae that obscure the view 

 of the main stem. 



In carrying out observations, the animal, after being washed in two or 

 three changes of filtered sea- water, is laid on a glass slide and a drop of 

 sea-water, free from any suspended particles, so placed as to wet the glass 

 all round the antennae. Trouble may be experienced on account of the 

 tendency of the creatures to jerk about and move out of the field, but if a 

 sufficient supply of the animals is at hand some will always be found to lie 

 quiet for a minute or two at a time. If it is necessary to keep the animals 

 absolutely still for a prolonged period, a simple plan is to use specimens 

 which have become asphyxiated by being innnersed along with many 

 others in an insufficient supply of water. If a dozen are kept in a small 

 dish of water overnight some will be found in the morning to be apparently 

 dead, having ceased to swim or to execute breathing movements. Many of 

 such apparently dead animals are alive, their heart continuing to beat, and 

 the circulation can now be watched with ease, for the animals continue 

 long in this narcotic condition. 



The blood flows in a very definite course in the anteunary filament. A 

 main artery leads down the filament ; this forms communications by means 

 of cross capillaries (one of which occurs opposite each joint) with a re- 

 turning vein, the system resembling a ladder in which the two main 

 vessels form the supporting poles while the connecting capillaries 

 correspond to the rungs. The existence of these vessels or channels is 

 inferred from the very definite path traversed by the blood corpuscles. It 

 is only exceptionally that the outline of the vessels themselves can be seen. 



From this arrangement it follows that the blood-flow is more rapid and 



