TRANSACTIONS Ol' THli SECTIONS. 155 



expiration. After tlioso movenieuts liad entirely ceased tliey still preserved the 

 same character and rhythm. 



From the fact thus proved that the rliythmical variations of arterial pressure and 

 pulse-frequency persist in the curarized animal after the respiratory nio\ements have 

 ceased, the author concludes that these movements cannot be regarded as their 

 cause; and he regards them both as attributable to rhythmical motor impulses 

 originating from the medulla oblongata, iu which the tliree centres which preside 

 over the respiratory movements and those of the circulation alike participate, viz. 

 the centre of the cardiac vagus, the respiratory centre, and the vasomotor centre. 

 He supposes that with each period of increased activity of the inspiratory centre a 

 period of increased activity of the vasomotor centre coincides, and that both of these 

 centres act antagonistically to the centre of the cardiac vagus. Each rhythmical 

 excitation of the respiratory centre determines corresponding excitation of the 

 vasomotor centre, which manifests itself in increase of arterial pressure and suspen- 

 sion of the activity of the cardiac vagus. 



The author adheres to the conclusion arrived at from his previous experiments 

 (Phil. Trans. 18G8), that in the do^ the respiratory movements of the chest exercise 

 a considerable direc.-t and mechanical influence on the heart, and thereby on the 

 arterial pressure. 



Experiments relatinrj to the Coagulation oftlie Blood. By E. A. Schafer. 



In the course of a series of experiments upon the coagulability of frog's blood, 

 performed in the Physiological Laboratory of University College, the author 

 observed the following facts : — 



The blood of the frog frequently exhibits, especially during the winter months, 

 but a very slight tendency to coagulate, so much so, that when drawn it not unfre- 

 quently remains completely liquid, with the exception of a film in immediate 

 contact with the sides of the glass vessel. On standing such blood soon separates 

 into two layers, the upper a clear plasma, the lower a mass of corpuscfes. If 

 undisturbed the blood may remain in this condition an indefinite time without 

 undergoing coagulation ; although if a little of the clear supernatant liquid be taken 

 up into a very fine glass tube it speedily solidifies, owing to the large relative 

 amount of surface to which it is exposed. 



In a few cases, on the other hand, the blood when drav\^l coagulates throughout. 

 If examined after a few hours it may appear as if coagulation had not occurred at 

 all, since we have the vessel filled, as before, with fluid blood separated into two 

 strata. In these cases, however, the clear supernatant liquid yields no further 

 coagulum in a tine glass tube, thus showing that it contains no fibrin in solutiouj 

 /. e. that it is scrum, not plasma ; besides, the contracted remains of the clot may 

 always be found. The appearance of reliquefaction of the blood here presented is 

 due entirely to the astonishing amount of contraction which the fibrin undergoes, 

 the result of this contraction being that not only the serum but even the corpuscles 

 themselves are expressed from its meshes*. 



That the diminution iu bulk of the clot (whicli may proceed to such an extent as 

 to leave but a slight trace) is due to this cause only, and not to a reliquefaction of 

 fibrin, as v. Recklinghausen supposed, is shown by the fact that when the primary 

 coagulation is complete no further coagulum is obtainable from the serum, even 

 under the most favourable circumstances. 



But there is a source of error to guard ao-ainst. The blood may appear to have 

 coagulatedthroughout, when all the while its central portions may not have par- 

 ticipated ; indeed this occurs in the majority of cases. It is easy to see that, under 

 such circumstances, when the fibrin contracts the serum which is expressed will 

 have mixed with it a greater or less amoimt of liquor sanguinis, and hence v>-ill be 

 found to be coagulable. 



* This process may readily be observed inicroscopically as it occurs in a very thin- 

 walled capillary tube. An immersion objective should "be used for the purpose of 



observation. 



