554 
a. o. ZWICK. 
Dia-pedesis .—Waller and Cohnheim have demonstrated it to 
be a fact that leucocytes can pass out of the vessels into the tis¬ 
sues, and this fact has a very important bearing on the phe¬ 
nomenon of phagocytosis just described. It can be observed by 
irritating the mesentery of a frog, when of course, all phenomena 
of inflammation follow, the first effect being an increase in the 
flow of blood through the affected region. If the irritation has 
been severe enough, or continues long enough, the current 
slackens, the corpuscles stagnate in the vessels, and inflammatory 
stasis is produced. The leucocytes adhere in large numbers to the 
walls of the capillaries, particularly the small veins, and then be¬ 
gin to pass slowly through them by ameboid movements, the 
passage taking place in the junction between, or it may be right 
through, the substance of the endothelial cells. And if these 
leucocytes happen to be loaded with tubercle bacilli, which for 
reasons given, they have been unable to digest, these bacilli have 
been implanted in the, to them, ideal culture-medium, the tissues 
of a living animal body. 
It is then plain: the absorbents, or lymphatics, gather the ba¬ 
cilli with the food material from the alimentary canal and trans¬ 
fer them to the different parts of the body, also pouring them out 
into the blood stream, and thus causing further dissemination. 
That such passage of the leucocytes can take place without the 
phenomena of severe local inflammation occurring, is undoubted; 
that it would most readily occur where the blood current is slow 
and the capillary network fine-meshed and intricate, is self- 
evident. 
The comparative slowness of the current and the disappear¬ 
ance of the pulse are the chief characteristics of the capillary 
circulation. The explanation is readily found in the great re¬ 
sistance offered by the narrow and much-branched vessels; the 
wider the bed, the shallower the stream, the slower the current. 
As Stewart says: “ The rivers of the blood are, even at their 
fastest, no more rapid than the sluggish stream. The mean ve¬ 
locity of a particle of blood in moving from the heart to the fem¬ 
oral artery does not, according to even the most liberal calcula- 
