1895.] MICROSCOPICAL JOURNAL. 307 



in our beautiful Cayuga Lake there is an animal, tlie 

 Necturus, with external gills through which the blood 

 circulates for its purification. So thin and transparent 

 is the covering tissue in these gills that one can see into 

 the blood stream almost as easily as if it were uncovered. 

 Every solid constituent of the blood, whether red cor- 

 puscle, white corpuscle, microbe or particle of dast, can 

 be seen almost as clearly as if mounted on a microscopic 

 slide. 



Into the veins of this animal was injected some lamp- 

 black mixed with water, a little gum arable and ordinary 

 salt, an entirely non-poisonous mixture. Thousands of 

 particles of carbon were thus introduced into the blood 

 and could be seen circulating with it through the trans- 

 parent gills. True to their duty, the white corpuscles 

 in a day or two engulfed the carbon particles, but for 

 several days more the leucocytes could be seen circu- 

 lating with the blood stream and carrying their load of 

 coal with them. Grradually the carbon-laden corpuscles 

 disappeared and only the ordinary carbon-free ones 

 remained. Where had the carbon been left ? Had it 

 been simply deposited somewhere in the system ? The 

 tissues were fixed and serial sections made. The nat- 

 ural pigment was bleached with hydrogen dioxid, so 

 that if any carbon was present it would show unmistak- 

 ably. With the exception of the spleen, no carbon 

 appeared in the tissues, but in many places the carbon- 

 laden leucocytes were found. In mucous surfaces and 

 on the surface of the skin were many of them ; in the 

 walls of organs were many more apparently on their 

 way to the surface with the load, that is the carbon is 

 actually carried out of the tissues upon the free surfaces 

 of the skin and mucous membranes, where, being outside 

 of the body, it could no more interfere in any way with 

 it. But what was the fate of the leucocytes that carried 

 the lampblack out of the tissues ? They carry their load 



