469 



The results mentioned are partly due to concentration of the 

 Ampere-turns near the air-gap and also to careful calculation and 

 design of all details; the theory of polar armatures') communicated 

 to the Academy, contributed its share to the result. 



Intestinal magnets. Incidentically tiie formulae for attractory arma- 

 tures were also given in the paper referred to. They show, that the 

 attraction of saturated ferromagnetic particles is a maximum for cones 

 with a semi-angle of 39°14', and for prisms of 30° ; for non- 

 saturated ferromagnetic or for paramagnetic substances these angles 

 are 42°11', and 32°8' respectively. According to the principle of 

 Faraday and Kelvin the attraction is determined by the gradient of 

 the first [second] power of the intensity .p of the field for the first 

 [second] group of substances. 



Some time ago Prof. Payk -) proposed a magnetic diagnosis, 

 prophylaxis and cure of peritoneal adhesions and similar deviations. 

 For this purpose a ferromagnetic intestinal filling is introduced either 

 per OS or per rectum. Then magnetic force is applied from outside 

 without the necessity of more or less dangerous laparotomy. At the 

 request of this well-known surgeon I was glad to collaborate in the 

 attempt towards a practical solution of this peculiar aitraction-\)Yoh\e^m ; 

 for a rational treatment of it the above-mentioned armature-theory is 

 absolutely necessary. The existence of an inditferent intermediate 

 zone and the necessity for exciting large attractive forces only beyond 

 this, characterizes this particular question. 



The ordinary type has a core of high permeability (of 12 cm. 

 thickness and 40 cm. length). It is somewhat concave at one end and 

 thus fits the average form of the human body. In the paper referred 

 to the formula is given for p, b.\>lbx and è'^S^Ibx'^ on the a:-axis 

 for the case of a segmental spherical armature and for that of a 

 concave paraboloid of re\olution. For the latter case it was shown 

 \ that a certain distance not before a maximum of the field was reached» 

 In this "neutral" point the gradient is zero and therefore the attraction 

 also vanishes ; the latter then increases, reaches a maximum and de- 

 creases again gradually. This distribution of the field is favoured by 

 the higher magnetisation at the periphery of the core compared with 

 that of the centre, which makes this case similar to that of hollow 

 cores. In the outset I even used a core with a conical bore in 

 order to allow an eventual radiologic transmission through it ; this 

 however proved later on to be practically unnecessary. A central 



1) H. DU Bois, These Proceediugs 15 p. 330, 1912. 



2) E. Payr, Munch, med. WochenscLr. 60 p. 2601, 1913. 



31* 



