288 O. HUG AND H. J. SCHLIEP 



analogy to the well-knowai strength-duration curve of the reaction to 

 electric stimulation. A similar close and dose-rate relationshi]^ has been 

 found in the immediate contraction of mammalian intestine under 

 irradiation (Hug, 1S)00; Schliep et al., 1961). The threshold of dose and 

 dose-rate varies considerably in different species and organs, and even 

 in individuals of the same species. 



However these observations did not permit us to draw definite con- 

 clusions with regard to the mechanism of action underlying these 

 immediate radiation effects nor to define the site of action. Behavioral 

 changes of Daphniae imder X-irradiation oliserved in the meantime 

 by Baylor and Smith (1958) are evidently due to effects on the Nauplius 

 eye of these animals. Therefore it must be taken into consideration 

 whether or not some of the effects observed by us are due to a similar 

 stinndation or disturbance of photoreceptors and may be compared 

 with the so-called roentgenphen in higher animals, recently investi- 

 gated by Lipetz (1955) in a very careful manner. Evidently not all 

 effects observed by us can be attril)uted to stimulation of photore- 

 ceptors but must be related to irritation of other parts of the nervous 

 system or other tissues. The reaction of a livmg animal as a whole, 

 however, seemed to be too complicated to clarify this question. 



EXPERIMENTAL 



Recently we have used isolated systems, e.g. nerve-muscle prepara- 

 tions to study the different jiarameters on which such immediate effects 

 may depend. Nerve-muscle preparations of the leech {Hirudo med. L.) 

 and of the earthworm {Lumhricus terr.) and isolated muscles of the leech 

 proved to be very sensitive to radiation and suitable for detailed 

 studies. 



Isolated strips of the ventral body wall still connected with the nerve 

 cord or isolated muscles, of both the species, were suspended vertically 

 to a lever, which registered the isotonic contractions on a smoked 

 drum. The preparation was kept in a moist chamber, rinsed continu- 

 ously by a modified Ringer-solution and aerated with air or oxygen or 

 a mixture of 95 per cent oxygen and 5 ]ier cent C'02. The specimens were 

 irradiated in this ])osition with 50 kV X-rays filtered by the ])erynium 

 window of the tube only. The doses and dose -rates given below are 

 measured in air at the site of the specimen. 



Nerve-muscle preparafions 



Two different effects could be observed : in a nerve-muscle ])reparation 

 showing spontaneous contractions irradiation can inhibit these con- 

 tractions temporarily (Fig. 1) and conversely, in a sj)ecimen that is 



