4 io SCIENCE PROGRESS. 



reckoned with, fitted in very well with the conceptions of 

 the neo-vitalists. 



Although Heidenhain's paper was only published in 

 1 89 1 there have been numerous researches on the same 

 subject published since. In some of these {e.g., Hamburger's) 

 Heidenhain's views are confirmed, while in other cases {e.g., 

 those of Cohnstein and Starling), Heidenhain's conclusions 

 are disputed, though there is no question as to the validity 

 of his experimental facts. 



In the review of this subject that now follows, I propose 

 to deal with these theories of lymph formation, restricting 

 myself, however, to a few of the typical researches, and not 

 attempting to give a resume of all the papers that have 

 appeared. It will be convenient to take this matter in the 

 following order : first to state Ludwig's original position, 

 then rapidly to pass through the various difficulties that 

 stood in the way of the full acceptance of his hypothesis ; 

 next to deal rather fully with Heidenhain's epoch-making- 

 research, and lastly, to consider the weighty objections that 

 Starling has urged against Heidenhain's views, and which 

 tell in favour of the older idea of Ludwig. 



Ludwig 1 speaks of the lymph flow as being conditioned 

 by two factors — first, differences in the pressure of the blood 

 in the capillaries and the fluid in the tissue spaces giving 

 rise to a filtration of fluid through the capillary walls, and 

 secondly, chemical differences between these two fluids, 

 setting up osmotic interchanges through the wall of the 

 blood-vessel. If the lymph is produced by a simple act of 

 filtration, then the amount of lymph must rise and sink with 

 the value of D — d, D representing the capillary blood 

 pressure, and d the pressure in the tissue spaces. 



In support of this mechanical theory, various workers in 

 the Leipzig laboratory showed (1) that increased capillary 

 pressure, due to obstruction of the venous outflow, increases, 

 the amount of lymph formed ; (2) that diminution of the 

 pressure in the lymph spaces, by squeezing out the lymph 

 previously contained in them, led to an increase in the 

 transudation. On the other hand, active hyperemia was 

 1 Lehrbuch der Physiologie, Bd. ii., p. 562 (2nd edit., 1861). 



