188 
Nephrocytes of Pediculus 
In his injection experiments Kowalevsky used various substances like 
ammonia-carmine, indigo-carmine, methylene blue, alizarine, and finally blue 
litmus on the advice of Metchnikoff. The employment of litmus was of special 
value since it showed that the pericardial cells possess an acid reaction, for, 
when the animal is injected with blue litmus the cells turn the absorbed 
litmus red. Kowalevsky therefore concluded that the pericardial cells con¬ 
stitute excretory accumulatory organs having an acid reaction. It may be 
noted here that the Malphigian tubes of insects possess a distinctly alkaline 
reaction. 
In 1892, Kowalevsky, whilst confirming his previous observations, found 
that the pericardial cells are incapable of taking up solid particles, these being 
taken up by lymphocytes or leucocytes only. 
The chief results of Kowalevsky were confirmed by Cuenot (1896) and 
Metalnikoff (1896). Subsequently Bruntz (1903) in his studies upon excretion 
in Arthropods, wherein he injected ammonia-carmine and indigo-carmine, 
was able to show that a great variation exists in the form, grouping and dis¬ 
tribution of the excretory cells to which he applied the name “nephrocytes .” 
He found these frequently situated at a distance from the heart and lying 
scattered between the lobes of the fat body. Finally, Keilin (1917) has de¬ 
scribed the nephrocytes in several species of dipterous larvae, and observed 
cases ( Lonchae vaginalis) where the nephrocytes under natural conditions 
were coloured, according to the age of the larva, either light brown or black by 
the accumulation within them of excretory substances. 
To determine the excretory function of the nephrocytes in Pediculus, it 
was necessary to employ one of two methods that have been used in similar 
studies upon other insects, the two methods being (1) to feed the insects with 
coloured fluid, or (2) to inject such coloured matter into their body cavity. 
Owing to lice being solely blood-sucking insects, we were obliged to carry out 
our experiments by the second method only. After a few preliminary trials 
we succeeded perfectly in obtaining satisfactory results, and, since it may 
prove useful to other investigators, we shall describe our method of performing 
such experiments. 
Method of performing Intra-coelomic Injection upon Pediculus. 
The first step is to prepare fine glass pipettes from tubes measuring 1 mm. 
in diameter and 7-8 cm. in length. One end of the tube is drawn out to a 
fine but rigid point which is broken off with a forceps under the binocular 
microscope so that a fine lumen can be discerned. 
The best results are obtained with lice maintained in the thermostat at 
30° C. for about 16 hours after a meal, replete lice being unsuitable for in¬ 
jection. Holding the louse between the forefinger and thumb of the left hand, 
the point of the pipette, charged with a small amount of injecting fluid and 
held in the right hand, is driven into the side of the insect’s abdomen, gentle 
pressure only being exerted. As soon as the point has traversed the external 
