318 ; The American Naturalist. [April, 
the different organs. Another great advantage in the study of 
the living leucocytes lies in their activity in the ordinary tem- 
perature of a room, a fact, which affords an opportunity for the 
close observation of the process of ingestion. By mixing on a 
slide a small drop of fresh blood or lymph with a small 
quantity of lamp-black suspended in normal salt solution, the 
taking up or ingestion of the carbon by the leucocytes can be 
seen to take place while they pass through their amoeboid 
hases. In a few hours the cells become filled with carbon 
particles (P1. IV), which are, however, contained exclusively in 
the cell body although appearances suggest their presence in 
the nuclei. ‘These latter parts also exhibit amoeboid forms (Pl. 
IV). By watching the cells carefully the granules are seen to 
move across the nuclei and gradually leave it clear, proving 
beyond doubt that they are in the cell body. 
In introducing the carbon into the living animals the follow- 
ing method was used. Into the abdominal cavity of the 
animals from 4-1 c. e. of a mixture of lamp black, gum arabic 
and normal salt solution was injected. Here it should be said 
that in these animals this cavity forms practically a great 
lymph space, in which the carbon is ingested by the leucocytes, 
the latter then pass into the blood circulation and from thatto 
the various organs and tissues. After periods varying from 4- 
10 days different animals were killed and the blood and tissues 
examined. In the case of Necturus, owing to the presence of 
external gills, the time of the appearance of the carbon-laden 
cells in the blood could be easily determined. By etherizing 
the animals and microscopically examining the circulation of 
the blood in the gill filaments once or twice a day the time of 
the appearance and also of the disappearance of ingested cells 
can be noted. The earliest appearance was on the 6th and the 
latest on the 9th days after injection. After 16 days a few 
scattered cells still remained. The results now given were 
chiefly obtained from a specimen of Cryptobranchus killed 10 
days after injection. 
In the microscopical examination of the tissues the ee 
difficulty encountered lay in the presence of a large amount 
natural pigment in the tissues. This is confusing both from 
