632 



PHYSIOLOGY. 



tion, and the less specialized tonic power alone 

 remains. The intermediate position of this 

 muscle is also shown in the duration of its vi- 

 tality after the death of the animal, which is 

 less than that of unstriped muscle, but decid- 

 edly greater than that of the ordinary striated 

 muscles. Evidence is accumulating that the 

 power of rhythmical contraction is common 

 to many different kinds of muscle ; and as it 

 has been developed to a greater extent in some 

 unstriated muscles than in others, so it has 

 reached a still higher stage that of rhythmi- 

 cal automatism in some kinds of cardiac mus- 

 cle than in others. We may, then, compare 

 the development of function in the three kinds 

 of muscular tissue as follows : 



Striated muscle of vertebrates : Rapidity of 

 contraction most highly developed ; tonicity 

 rudimentary; rhythmic action still more rudi- 

 mentary. 



Cardiac muscle: Khythmic action most high- 

 ly developed ; rapidity of contraction well 

 marked ; tonicity well marked. 



Unstriped muscle : Tonicity most highly de- 

 veloped ; rhythmic action well marked ; rapidi- 

 ty of contraction most rudimentary. 



Stimulation of the vagus nerve was found 

 capable of producing opposite effects upon the 

 rhythm of the heart, either of slowing, or stand- 

 still, or of acceleration. The results are more 

 constant with the tortoise, where a stand-still 

 can always be obtained, frequently followed 

 by acceleration, but not accompanied by evi- 

 dence of a primary acceleration, than with the 

 frog. The effects are almost exclusively pro- 

 duced through the fibers of the right vagus 

 nerve. The auricular contractions only are af- 

 fected by the stimulation, and this by being 

 diminished in strength during its operation, 

 and increased after it has been stopped. Nerv- 

 ous action has an effect competent both to de- 

 press and to exalt the conduction power of the 

 muscular tissue of the auricle, and that inde- 

 pendently of the action upon the force of the 

 muscular contractions. It removes a partial 

 block, and enables every contraction to pass 

 the blocking-point by expediting the recovery 

 of the conduction power of the muscle at that 

 point, which would otherwise take place more 

 slowly after the passage of each contraction- 

 wave. While the initial effect of the vagus 

 appears to be to depress some function, its final 

 and most enduring power is to exalt, intensify, 

 and repair that function. It may, therefore, 

 be regarded as essentially the trophic nerve of 

 the heart. Its effects on the contraction force 

 and conduction power of the cardiac muscle 

 are the same as those of an interrupted current 

 applied to the muscle directly, which is too 

 weak to cause muscular contractions. Atropine 

 improves the contraction power, the rhythmi- 

 cal power, and the conduction power of the 

 muscle, in a fixed and stable manner, but not 

 necessarily lastingly. Muscarine depresses every 

 function, but without preventing the possibili- 

 ty of a limited amount of improvement in it. 



Messrs. II. H. Donaldson and Lewis T. Ste- 

 vens, of Johns Hopkins University, have found, 

 from experiments with digitaline on the heart 

 of the frog and the terrapin, that the drug 

 causes a decrease in the work done by the 

 heart, that in moderate doses it increases the 

 blood-pressure, and that it causes a rise of 

 mean blood-pressure by constricting the arte- 

 rioles, probably through its action on the mus- 

 cular coats. 



Taljanzeff states that, in violent breathing, 

 partial or complete inhibition of the contrac- 

 tions of the right side of the heart may take 

 place, without, however, any fall of arterial 

 pressure resulting, the blood being forced from 

 the right to the left side of the heart by the 

 action of the breathing movements on the or- 

 gan, especially on the right ventricle. He has 

 discovered also that, if the branches of the 

 vagus going to the lungs are cut, and their cen- 

 tral ends stimulated, a decided reflex action on 

 the heart and blood-vessels is obtained. In 

 most cases the heart was slowed, giving the 

 well-known "vagus-pulse," and the blood- 

 pressure was lowered ; though in one experi- 

 ment there was a fall of aortic pressure, with- 

 out any change in either the force or the rate 

 of the heart contractions. 



Gaule has shown that a frog's heart, washed 

 out with dilute solution of common salt until 

 it ceases to beat, is rendered capable of further 

 pulsation when dilute alkaline solutions are 

 sent through it; and he concludes that the al- 

 kali nourishes the heart. Martius, while con- 

 firming the experiment, dissents from the con- 

 clusion. The administration of the alkali, he 

 finds, leads to a certain number of beats, but 

 these soon cease, and a fresh supply of alkali 

 is then inefficient, while other liquids, espe- 

 cially blood-serum, lead to renewed cardiac 

 contractions. In his opinion, the frog's heart- 

 muscle has in itself no store of energy-yielding 

 material which it can call upon, but works at 

 the expense of food-matters yielded it con- 

 stantly by the liquid circulating through it. 

 When the heart, irrigated with salt solution, 

 ceases to beat, this is due to the saturation of 

 its tissue with carbon dioxide, while still some 

 nutrient matter (blood) remains not washed 

 out from the ventricular net-work. The salt 

 solution, acting merely as a medium for physi- 

 cal diffusion, can not remove the carbon dioxide 

 as fast as it accumulates, and consequently the 

 heart ceases to beat while it still has some 

 available food. The alkali, on the other hand, 

 chemically removes the injurious carbon diox- 

 ide ; and the heart beats for a short time, using 

 the food-stuff in the blood still present in its 

 meshes. When the heart, treated with dilute 

 alkali, ceased to beat, new pulsations could 

 only be obtained by supplying it with liquids 

 containing serum-albumen. 



The Blood. Several independent observers 

 describe' a new morphological element of the 

 blood different in character from both the 

 white and red corpuscles, and believed to be 



