118 



SCIENCE. 



[N. S. Vol. III. No. 56. 



pointed out, reasons for considering which 

 undemonstrated were given. 



19. H. G. Beyer: 0?i the influence of 



exercise on growth. 



Dr. Beyer spoke of the necessity of apply- 

 ing more exact methods of investigation to 

 the study of this very important physiologi- 

 cal subject than had been done hitherto. 

 While acknowledging that some of the more 

 general good eflects of all forms of exercise 

 were within the easy reach and the experi- 

 ence of all, the more remote and permanent 

 ones must be made the subject of more 

 serious study and investigation. 



He described one of the methods by 

 means of which the influence of systematic 

 gymnastic or of other forms of exercise might 

 be ascertained, and presented the results of 

 some investigations in this direction. For 

 example, as to height, his figures presented 

 strong evidence that height is decidedly 

 increased by exercise taken within physio- 

 logical limits and during the period of 

 growth. 



20. W. H. Howell (for Messrs. Conant 

 and Clark): The existence of a separate in- 

 hibitory and accelerator nerve to the eraVs 

 heart. 



The work was done upon the common 

 edible crab, Callinectes hastatus. The authors 

 have been able to show that two separate 

 nerves pass from the thoracic ganglion to 

 end in a plexus in the wall of the peri- 

 cardium and that one of these nerves, when 

 stimulated, inhibits the heart beat, while 

 the other causes marked acceleration. The 

 inhibiting nerve was traced anatomically 

 to the ganglion, which it joins in company 

 with the large mandibular nerve. The 

 junction of the accelerator nerve with the 

 ganglion has not so far been demonstrated 

 anatomically, but the physiological evidence 

 indicates that it leaves the ganglion in 

 company with the nerve to the first pereio- 

 pod. If this latter nerve is severed from the 



ganglion, stimulation of the ganglion no 

 longer gives acceleration. If the peripheral 

 end of the severed nerve, however, is stimu- 

 lated, marked acceleration is obtained. If, 

 moreover, the severed nerve is again cut a 

 little farther to the periphery, stimulation 

 of the new periphei-al end no longer affects 

 the heart, while stimulation of the small 

 isolated piece thus obtained gives accelera- 

 tion. This evidence indicates that the ac- 

 celerator nerve leaves the nerve of the first 

 pereiopod a short distance, about 1 centi- 

 metre, beyond the thoracic ganglion. As 

 stated above, in the neighborhood of the 

 pericardial plexus it is easily found as a 

 separate nerve lying close to the inhibitory 

 nerve. The authors were not able to obtain 

 any evidence of a tonic activity of either of 

 these nerves. Stimulation of the cerebral 

 ganglion with strong currents gave inhibi- 

 tion of the heart, which disappeared, how- 

 ever, when the commissures connecting 

 this ganglion with the thoracic ganglion 

 were cut. 



21. Fr. Pfafp: On toxicodendrol and on 

 the so-called toxicodendric acid. 



' Toxicodendric acid ' has been regarded 

 heretofore as the active principle of poison 

 ivy, Rhtis toxicodendron. Dr. Pfafi" isolated 

 this acid and analyzed its barium and 

 sodium salts. Quantitative and qualitative 

 tests show that it is really nothing but 

 acetic acid. The true active principle of 

 poison ivy is an oil named by Dr. Pfaff 

 Toxicodendrol. The purity of the oil ob- 

 tained was proved by quantitative analyses 

 of the lead compounds with different prepa- 

 rations of the oil. 



22. H. C. Chapman : Methods of teaching 

 physiology. 



Professor Chapman gave a demonstrative 

 talk upon methods employed in his own 

 teaching, illustrating his remarks largely by 

 apparatus devised bj^ himself He urged 

 the value of the comparative method and 



