June 11, 1897.] 



SCIENCE. 



907 



tion of the vagus the heart can be kept 

 beating at a remarkably slow rate for some 

 time and yet the blood pressure remain 

 near or even rise above the normal. 



(2) Depressor. In most cases there is a 

 separate depressor nerve ; it is usually 

 formed bj' two roots, one from the superior 

 laryngeal nerve, and the other from the 

 ganglion of the trunk of the vagus. Stimu- 

 lation of this nerve gives results entirely 

 similar to those observed in the rabbit, viz., 

 fall of blood pressure and a reflex slowing 

 of the heart. 



(3) Accelerator nerve. The anatomical re- 

 lations of these nerves resemble in general 

 those found on the dog ; stimulation of them 

 causes marked increase in the heart rate 

 and very frequently irregularity of the 

 ventricles from their failure to follow all the 

 auricular beats. Stimulation of the ac- 

 celerators while the heart is being slowed 

 by stimulation of the vagus causes an in- 

 crease in the heart rate. 



Some Experiments on the Lohsterh Heart. Eeid 



Hunt. Read by title. 



I. Some General Properties of the Cardiac 

 Muscle of the Lobster (with Messrs. Book- 

 man and Tierny). 1. The latent period 

 caused bj' electrical stimulation is very 

 short, varying according to the condition 

 of the heart from 4^ to -j-if, of a second. 

 2. The heart responds to stimulation dur- 

 ing every phase of a contraction, whether 

 this is spontaneous or has been caused by 

 previous stimulation, i. e., there is no re- 

 fractory period (the latent period, however, 

 was not investigated as to this point). 3. 

 A true summation of contractions is easily 

 produced ; one contraction can be super- 

 imposed upon another until the resulting 

 contraction is many times higher than 

 any single (maximal) contraction. 4. Com- 

 plete tetanus is readily produced, as has 

 been observed by Howell for the crab's 

 heart ; the number of stimuli necessary to 

 produce it varies greatly according to the 



condition of the heart, 4 to G per second 

 being sufficient as a rule. 5. The height 

 of the contraction varies (up to a maxi- 

 mum) with the strength of the stimulus, 

 i. e., the ' all or nothing ' law does not hold. 



II. 27(6 Effect of Changes of Temperature 

 upon the Lobster^s Heart (with Messrs. 

 Lyman and Williams). Most of the re- 

 sults were obtained with hearts removed 

 from the bodj^ and placed in the lobster's 

 defibrinated blood ; the temperature of the 

 blood could be altered as desired. The 

 force and frequency of the beat increased 

 as the temperature was lowered from that 

 of the room (18° C.) to about 13° C, which 

 seemed to be, as a rule, the optimum tem- 

 perature for hearts in the body as well as 

 for the isolated ones. As the tempera- 

 ture was lowered still farther, the beats 

 became more rapid but feebler; the tem- 

 perature was not carried below 2° C, but 

 the heart beat well at this temperature. 

 When the temperature was raised above 

 the optimum, the beats became fewer and 

 irregular and the heart went into heat 

 standstill at a remarkably low temperature ; 

 upon cooling it beat again, unless it had 

 been exposed to a too high temperature. 

 The temperature at which a standstill 

 occurred varied according to the condi- 

 tion of the heart ; previous cooling and 

 long exposure caused it to occur at very 

 low temperatures. The heart was never 

 observed to beat above 22° C, although 

 it responded to electrical stimulation up 

 to 27°. The crab's heart goes into stand- 

 still at a much higher temperature (45- 

 50° C). Sudden changes of temperature 

 caused a temporarj' acceleration. A moder- 

 ate degree of tension on the heart caused a 

 much more rapid beat. 

 The Innervation of the Heart of the Guinea Pig. 



D. W. Harrington. 



In the guinea pig the avei'age blood pres- 

 sure in the carotid arterj' is 78.25 mm. of 

 mercury ; the average rate of heart beat, 



