1871.] Blood-corpuscles through the Walls of the Vessels. 563 



accomplished by pressure from within. It is easy to see that the manner 

 or degree to which the corpuscle or body coheres to the film will deter- 

 mine very materially the method of its transmission. 



All, then, that is essential for a rigid or plastic body to pass through a 

 colloid film is : — 1st, an intimate power of cohesion, either mediately or im- 

 mediately, between the film and the body ; 2nd, a certain amount of pres- 

 sure from within ; 3rd, power in the substance of the film to cohere to 

 the surface of the body (or to some intermediate matter which already 

 coheres to the surface) during its passage ; 4th, cohesive plasticity of the 

 particles of the material of which the film itself is composed, so that the 

 breach in it may again become reunited as it descends upon the opposite 

 surface of the body which is being extruded. 



It is quite remarkable to how great an extent these conditions appear to 

 be complied with in the passage of the white corpuscle through the capil- 

 lary wall, as affirmed by independent observers. 



In the factitious examples by which I have sought to illustrate these 

 effects, the film moves over the body, or the body through the film, by 

 virtue of the intermediate agency of the solution which has cohesive at- 

 traction for both ; and the film does not rupture, because, while the 

 body is travelling through, it can continue to cohere till such time as it 

 is brought again into contact with its own particles at the opposite pole of 

 the extruded body. 



Theoretically, as it leaves the sphere or protruding body, the aperture 

 should gradually narrow to absolute union at a focal point, or, according to 

 the laying-down view, having resealed itself from the bulb ; practically, 

 however, I find that the film rarely leaves the bulb or sphere without form- 

 ing on it a small hemispherical bubble, which is large in the ratio of the 

 rapidity with which the detachment is effected. 



If detached with very great care, the bubble is exceedingly small ; but 

 I could not succeed with a spherical bulb in getting rid of it altogether ; 

 with a more conical bulb, however, this was readily effected. In the 

 case of the sphere, the film is in reality drawn out into a little neck, 

 as in the other examples in which continuity is effected ; and this neck 

 is pulled into two, and both parts cohering at the point of severance, we 

 get on the one side the perfected film, and on the other a small enclosure 

 of air which takes on the hemispherical form. This is owing to the 

 annular contraction of the tubular part. If the body were small or 

 less spherical, or the film a trifle more rigid, this would not occur. I find, 

 in fact, by experiment that smaller bodies, more conical in their termina- 

 tion, do not do this, but draw out a kind of streak of solution as they 

 leave the film — a fact I have often observed with the white corpuscles. In 



experiments, is brought into contact with one point of its convexity, the ball is at onco 

 drawn into the film as far as its equator, and is compelled to retain this position in 

 opposition to the force of gravity. This is the exact converse of the case of the fixed 

 bulb, in which the attraction is satisfied at the expense of the expansibility of the film. 



2x2 



