105 



evidenced after teatment by veratrine. It must be recollected, 

 however, that veratrine, besides its action upon vertebrate 

 striated muscle, also jDaralyses nerve fibres. It is possible that 

 its action upon the fly's intestine, therefore, is due to paralysis 

 of nervous conduction rather than to direct action upon the 

 muscle fibres. 



Of the drugs which affect myoneural junctions, adrena- 

 line, as is well known, stimulates the junctions of the 

 postganglionic fibres of the autonomic system. Where sympa- 

 thetic stimulation causes muscular contractions or increase of 

 tone, adrenaline will give rise to like effects, as in the blood 

 vessels and the heart, the muscularis mucosoe and the spleen 

 (13, 14). Where sympathetic stimulation causes loss of tone 

 and inhibition of contractions adrenaline elicits similar 

 responses, as in the muscles of the bronchi and the external 

 muscular coats of the intestine. Ergotoxine stimulates cer- 

 tain motor myoneural junctions, particularly those of the 

 blood vessels, heart, and uterus. It has little action upon the 

 mammalian intestine. Ergotinine is the anhydride of ergo- 

 toxine, and has comparatively little action upon mammalian 

 myoneural junctions. Ergamine acts directly upon the muscle 

 cells themselves, causing loss of tone in some (blood vessels) 

 and increase of tone in others (uterus and bronchi), while it 

 gives rise to energetic peristalsis of the mammalian intestine 

 ("peristaltic rush'^). Digitaline stimulates the inhibitory 

 myoneural junctions in the heart and also stimulates (increases 

 the tone of) the muscle cells themselves. 



In their effects upon the fly's intestine these drugs fall 

 into two groups which are sharply opposed to one another. 

 The first, represented by adrenaline, inhibits rectal and stimu- 

 lates intestinal contractions.; the second, comprising ergotinine, 

 ergotoxine, ergamine, and digitaline, inhibits both rectal and 

 intestinal contractions. 



Tlie action of adrenaline upon this preparation is most 

 characteristic and invariable. It exactly reproduces the effect 



of increasing the^ ratio; in other words, the preparation sub- 



Ca 

 jected to the action of adrenaline behaves as if the ^^ thresh olds 



Ca 

 had been lowered. A mixture in which the ^^^ratio had formerly 



been insufficiently high to permit intestinal peristalsis now not 

 only facilitates peristalsis but also inhibits rectal contractions. 

 This action of adrenaline is illustrated by the following pro- 

 tocols, which are typical of many experiment's. In each case 



