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exact and comprehensive and is as follows: "It will be perceived that the 

 blood poured into the right auricle is mostly impure or venous, that poured 

 into the left fully aerated or arterial. When the auricles contract, which 

 they do simultaneously, each passes its blood into the corresponding part 

 of the ventricle, which then instantly contracts before the venous and ar- 

 terial bloods have time to mix. Since the conus arteriosus springs from 

 the right side of the ventricle, it will at first receive only venous blood, 

 which, on contraction of the conus, might pass either into the bulbus aortae 

 or into the aperture of the pulmo-cutaneous trunks. But the carotid and 

 systemic trunks are connected with a much more extensive capillary sys- 

 tem than the pulmo-cutaneous, and the pressure in them is proportionately 

 great, so that it is easier for the blood to enter the pulmo-cutaneous trunks 

 than to force aside the valves between the conus and bulbus. A fraction 

 of a second is, however, enough to get up the pressure in the pulmonary 

 and cutaneous arteries, and in the meantime the pressure in the arteries 

 of the head, trunk, etc., is constantly diminishing owing to the continual 

 flow of the blood toward the capillaries (sic). Very soon, therefore, the 

 blood forces the valves aside and makes its way into the bulbus aortae. 

 Here again the course taken is that of least resistance ; owing to the 

 presence of the carotid gland the passage of blood into the carotid trunks 

 is less free than into the wide elastic systemic trunks. These will there- 

 fore receive the next portion of blood, which, the venous blood having 

 mostly been driven to the lungs, will be a mixture of venous and arterial. 

 Finally, as the pressure rises in the systemic trunks, the last portion of 

 blood from the ventricle, which, coming from the left side, is arterial, will 

 pass into the carotids and so supply the head." 



It will be seen on critical examination of this scheme that several 

 points are open to argument even if we grant the segregation of bloods in 

 the spongy ventricle : 1, the element of time ; 2, the mechanics ; 3, the com- 

 parative anatomy ; and 4th, the experimental evidence. 1. The frog's heart 

 under normal conditions beats about GO to the minute with a ventricular 

 systolic phase of about 0.2 sec. Now if one reads the description, bear- 

 ing in mind that the whole process is completed in one-fifth of a second, 

 and that all this is inferred in order that the head shall receive a better 

 blood supply, one is tempted to hold one's breath. The time is short and 

 much must be accomplished. If the blood in the systemic arteries is being 

 forced toward the capillaries, what is holding it back in the pulmo-cu- 

 taneous and carotid trunks? Again the regulation of the valves and re- 



