May 28, 1897.] 



SCIENCE. 



821 



formance of greater work. It seems clear 

 that this law applies to the muscle of the 

 heart, as well as to voluntary miiscle. "We 

 do not know precisely how increased 

 tension facilitates the expenditure of 

 greater muscular energy. 



Another well-known fact in the me- 

 chanics of muscle is of importance in this 

 connection. With increase of muscular 

 tension under a given stimulus, a point is 

 reached where the extent of contraction is 

 diminished, although the mechanical work 

 done, determined by multiplying the 

 height to which the load is lifted by the 

 weight of the load, is increased. This law 

 applied to the heart, whose contractions 

 are alwaj'S maximal for the conditions 

 present at any given time, signifies that, 

 with increased resistance to the contraction 

 of the muscular wall of one of its cavities, 

 this cavity will empty itself during systole 

 less completely than before. In other 

 words, dilatation occurs, and, as has been 

 shown by Roy and Adami, to whom we 

 owe important contributions on this as well 

 as on many other points relating to the 

 mechanics of the heart, dilatation regularly 

 antedates hypertrophy. This primary dila- 

 tation, however, is not to be looked upon 

 as evidence of beginning heart failure, for, 

 as these investigators pointed out, it is 

 within limits only an exaggeration of a 

 physiological condition, and can be subse- 

 quently overcome by hypertrophy which, 

 in consequence of increase in the sectional 

 area of the muscle, lessens the strain upon 

 each fibre, and thereby permits it to shorten 

 more during contraction. If this result is 

 completely secured we have simple hyper- 

 trophy. More often the dilatation remains, 

 and must necessarily remain, and we have 

 excentric hypertrophj'^, which secures, for a 

 time at least, adequate, but I do not think 

 we can say perfect, compensation. 



The weight of existing evidence favors 

 the view that the power of the heart to 



adapt its work to the resistance offered re- 

 sides primarily in its muscle-cells, and not 

 in intrinsic or extrinsic nervous mechan- 

 isms, although doubtless these latter in 

 various ways, which cannot be here con- 

 sidered, influence and support this regu- 

 lating capacity. Nor can I here pause to 

 discuss the influence of blood-supply to the 

 cardiac muscle upon the force of ventricular 

 contraction, although Porter has demon- 

 strated that this is important. 



In tracing the steps from the primary 

 morbid condition to the final hypertrophy, 

 we have thus far had to deal mostly with 

 known mechanical factors. We now come 

 to the question, How does increased func- 

 tional activity lead to increased growth ? 



Inasmuch as greater functional activity 

 is regularly associated with a larger supply 

 of blood to the more active part, the view 

 is advocated by many that the increased 

 growth is the direct result of this hypere- 

 mia, and one often encounters, especially 

 in biological literature, this opinion ex- 

 pressed as if it were an indisputable fact. 

 There is, however, no conclusive proof of 

 this doctrine, and many facts speak against 

 it. The examples from human pathology 

 commonly cited to support the doctrine 

 that local active hypersemia incites growth 

 of cells are, so far as I am able to judge, 

 complicated with other factors, such as in- 

 jury, inflammation orti'ophic disturbances. 

 Transplantation-experiments, such as John 

 Hunter's grafting the cock's spur upon 

 the cock's comb, sometimes adduced in this 

 connection, are not decisive of this question, 

 for here a new circumstance is introduced 

 which some suppose to be the determining 

 one for all morbid cell-growth, namely, the 

 disturbance of the normal equilibrium be- 

 tween parts. Local active hyperjemia may 

 exist for a long time without evidence of 

 increased growth in the congested part. 

 To say that the hyperaemia must be func- 

 tional is at once to concede that it is not 



