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sistance to the flow of blond must indeed be very minutely adjusted to 

 separate the venous from a mixed and a mixed from an arterial blood 

 issuing from the same opening with say, one-fifteenth of a second to accom- 

 plish each phase. 2. Further the tracings made by Gompertz show that the 

 blood reaches the pulnio-cutaneous and aortic trunks at the same time and 

 under the same pressure. Still further the inspiration in the frog in- 

 creases, not decreases, the intrathoracic pressure and would retard the 

 pul mo-cutaneous system, and it has not been demonstrated satisfactorily 

 to my knowledge that the capillary system of the pul mo-cutaneous vessels 

 is actually less developed than in the systemic area. 3. The comparison 

 of the various types of amphibian circulation is of interest. Bruner (1), for 

 example, makes the following statement : "The fact that the septum 

 atriorum disappears with the lungs indicates clearly that in the sala- 

 manders with lungs the septum performs a certain function which becomes 

 superfluous or impossible after the loss of these organs. This function is 

 the separation of the venous blood of the right auricle from the aerated 

 blood of the left auricle. But 'what is the significance of this separation 

 if the two sorts of blood are afterward mixed during the passage through 

 the ventricle and conus? Or is there, after all, in salamanders with lungs 

 a partial separation of the aerated and the venous blood in its entire course 

 through the heart? Such a separation occurs, as is well known, in the 

 heart of Rana. Now as regards the atrium and ventricle, we find essen- 

 tially the same structure in Salamandra as in Rana. It is true that the 

 septum atriorum in the salamander is perforated, while in the frog it is 

 not. But during the brief stay of the blood in the auricles the small per- 

 forations which have been described would permit little mixing of the 

 blood. There would be much better opportunity for this to occur in the 

 ventricle, but here we have the same spongy condition in Salamandra and 

 Rana. So far then, Rana does not seem to have a decided advantage over 

 the salamander in respect to the separation of venous and arterial blood 

 in the heart. We may therefore conclude that in the salamander, as in 

 Rana, the first blood passing from the ventricle into the conus during the 

 ventricular systole is chiefly venous. In Rana this is directed into the 

 pulmonary artery. In the salamander, however, the structure of the 

 conus does not indicate that it could influence the direction of the blood 

 current. We must turn, then, to the bulbus arteriosus and the great ar- 

 terial vessels for further light on our problem." "The spiral valve of the 

 Falamanders can have no control over the direction of blood which passes 



