206 INTRODUCTION TO THE WORMS 



In cases of heavy infection it is usually possible to find the eggs 

 in the faeces or other excretions by simple microscopic exam- 

 ination of a smear made directly from the faecal sample. Many 

 light infections, however, escape detection by this method, and 

 various means of concentrating the eggs so that they can be more 

 readily found have been devised. One method of concentration 

 is to mix with water, strain, and centrifuge, thus eliminating 

 coarse material and throwing the relatively heavy eggs to the 

 bottom of a tube. The principal objection to both methods is 

 the small size of the sample which is examined. 



Several methods for the quick and efficient examination of 

 large samples of faeces have recently been devised. One method, 

 known as the glycerine-salt method, developed by Barber, con- 

 sists in thoroughly mixing a fairly large faecal sample with a mix- 

 ture of equal parts of glycerine and saturated magnesiun sul- 

 phate solution. The eggs present float to the surface and can 

 be poured off on large slides for examination. By centrifuging 

 negative specimens and again floating the eggs in a glycerine-salt 

 solution a still higher percentage of positives can be found. In 

 a test trial in Siam 35.5 per cent of 45 faecal samples were found to 

 be hookworm-infected by examination of two slides by the plain 

 smear method, whereas 84.4 per cent were positive by the exam- 

 ination of a single slide by the glycerine-salt method, and 86.6 

 per cent by examination of two slides. 



A still more accurate method is the brine flotation-loop method 

 of Kofoid and Barber. A large faecal sample is thoroughly mixed 

 with concentrated brine in a paraffin paper container of two or 

 three ounces capacity. The coarse float is forced below the 

 surface by means of a disk of No. 9 steel wool, and the container 

 is allowed to stand an hour for the eggs to float to the surface. 

 The surface film is then wiped off with wire loops one-half inch 

 in diameter, the material transferred to a large slide, and exami- 

 nation made. The number of positives escaping detection by this 

 method is practically negligible. Another very simple and effect- 

 ive method is to mix the faecal sample thoroughly with a con- 

 centrated salt solution in a container so filled that there is a slight 

 meniscus. After standing a few minutes the eggs rise and adhere 

 to a glass slide touched to the surface of the meniscus. This 

 method is very effective especially for hookworm eggs, but is 

 said not to be useful for operculated eggs or for larvae. 



