148 University of California Puhlications in Zoology [Vol. 18: 



A general rule may be laid down here at this time. The ether 

 tends at first to settle the emulsion temporarily, but at the end of 

 about two minutes the emulsion begins to rise up and foam again 

 because the ether becomes localized by absorption in the debris. In 

 order then to get the best results and to be assured of the greatest 

 possible flotation of ether-soaked debris, one should cease stirring at 

 the very moment the emulsion commences to foam again. Then the 

 emulsion should be hurried into a separatory funnel and allowed to 

 stand for at least five to seven minutes, during which the cysts will 

 settle to the bottom in the saline solution and debris will float in the 

 ether above. The funnel used for this separation has a funnel-shaped 

 bowl with steep sides contracting to a narrow neck above the turn- 

 cock. 



At the end of this period of standing, the saline solution, about 

 fifteen cubic centimeters, is drawn off at the bottom of the separatory 

 funnel into a centrifuge tube of a capacity of fifteen cubic centimeters,, 

 and is centrifuged for three minutes at 1600 revolutions per minute. 

 The supernatant fluid is then drawn off and the residue is examined 

 microscopically for the cysts. At this time a drop of neutral red is 

 applied to a small amount of this residue preparatory to microscopic 

 examination if the stain has not been used previously. It is preferable 

 to use it at this time in order to procure a sharper contrast between 

 the cysts and the surrounding debris. 



By this method a faecal examination can be completed in twenty- 

 five to thirty minutes, which is considerably less than the time required 

 by the method which Cropper and Row (1917) described. Although 

 I have been especially interested in the application of this modification 

 of their method to the detection of the cysts of Giardia, I have noticed 

 at the same time that it is equally applicable to the detection of cysts 

 of Entamoeba, of other flagellates, and of the eggs of nematodes, which 

 I have found in the faeces of the rat. 



The great value of this method of concentrating cysts of protozoan 

 parasites is realized when one desires the most accurate diagnosis of 

 a suspected case. 



A high degree of infection by both amoeba and flagellates is 

 reported by Dobell (1917) from both dysenteric and non-dysenteric 

 convalescents from the Mediterranean area in British hospitals. Each 

 infected individual might become the source through unsanitary con- 

 ditions for further distribution of the disease among the troops should 

 he return to the front, or possibly to civilians on his return to private 



