SCIENCE 



[N. S. Vol. XXX. No. 776 



parasites by causing the pyriform stages to 

 disappear quickly and also to cause the total 

 disappearance of the parasites from the periph- 

 eral blood. The action was most noticeable 

 on the pyriform stage found in the plasma, 

 which is exactly analogous to the action of 

 quinine in malaria. However, the drugs ap- 

 parently reached the stages within the cor- 

 puscles, causing them to show signs of degen- 

 eration. They presented a ragged and irreg- 

 ular appearance, quite different from the 

 normal. 



In the experiments with trypanblau ten dogs 

 suffering with piroplasmosis were utilized. 

 Failure to cure the disease resulted in only 

 three out of the ten cases. In the failures 

 distemper and other factors probably con- 

 tributed to the death of the animals. This is 

 especially likely in view of the effect noted 

 upon the morphology of the organism in the 

 microscopical examinations. In one case, 

 which was repeated successfully, an injection 

 of trypanblau twenty-four hours after inocula- 

 tion prevented the appearance of the parasites 

 in the blood of the dog which remained per- 

 fectly well. 



In a note appended to the paper we are in- 

 formed that trypanblau exerts a very prompt 

 effect on the parasites of splenetic fever. This 

 effect is precisely similar to that on the organ- 

 ism of the dog disease with which the experi- 

 ments were primarily concerned. It is thus 

 permissible to assume that the agents used by 

 Messrs. Nuttall and Hadwen may be of use in 

 the treatment of this very important disease, 

 as well as in others caused by similar organ- 

 isms. We are informed that the authors have 

 interested the Colonial Office and the Depart- 

 ment of Agriculture and Fisheries in extensive 

 practical tests. We are promised reports upon 

 this work and upon further laboratory experi- 

 ments at an early date. 



The writer commends the paper as one of 

 far-reaching importance. Moreover, it is a 

 model in the treatment of an intricate subject. 

 Full details of experiments are given so that 

 the reader knows exactly what are the bases 

 for the conclusions drawn. 



W. D. Hunter 



U. S. Department of Aqeicultuee 



SPECIAL ARTICLES 

 DEMONSTRATIONS WITH THE MUSICAL ARC 



The musical arc offers a convenient means 

 of demonstrating many important features of 

 electromagnetic theory. It may be of interest, 

 therefore, to give a brief description of appa- 

 ratus and methods, with references to some of 

 the more elementary experiments which have 

 been found helpful. 



As is well known, the musical or " sing- 

 ing " arc' is obtained by connecting in paral- 

 lel with the direct current arc a system con- 

 taining seH-induction and capacity. The arc 

 used without this parallel or " secondary " 

 system may be more or less unsteady, show- 

 ing at the poles sudden change of potential 

 difference of considerable magnitude. The 

 secondary system may be thought of as sup- 

 plying the conditions for taking up these 

 fluctuations, and, in turn, emitting electric 

 oscillations of frequencies determined in large 

 part by the secondary itself. These oscilla- 

 tions, reacting on the arc, cause fairly regu- 

 lar interruptions in the discharge, which 

 therefore emits a musical note. The pitch of 

 this note may be varied by changing the con- 

 ditions of the arc-circuit as well as by vary- 

 ing those of the secondary. 



Examination by a revolving mirror and by 

 the spectroscope seems to confirm what might 

 from general considerations be expected in an 

 arc of this kind, viz., that although the arc is 

 interrupted, the poles give the distinctly dif- 

 ferent and characteristic forms of discharge 

 observed in the continuous arc.^ 



For purposes of demonstration, good results 

 may be obtained by using a condenser with 

 capacity which may be varied from 1 to 10 

 microfarads and which is capable of standing 

 a potential difference of 1,000 volts. The coil 

 for the secondary may be made with three 

 hundred turns of No. 15 annunciator wire 

 wound on a spool of 10 cm. radius and 3 cm. 

 axial length. The arc is perhaps most easily 

 maintained between carbon poles. Examined 



^Duddell, Electrician, 46, 1900. Simon, Pliys. 

 Zeit., VII., 1906. Austin, Bulletin of Bureau of 

 Standards, 3, No. 2, 1907. 



''Vide Astrophysical Journal, XXVIII., No. 1, 

 1908. 



