108 



intestine, tlierefoi-e, react to these drugs in a manner corre- 

 sponding to tlieir function rather than to their structure. 

 The effects of these drugs may be classified in relation 



to the-^ gradient which has been shown to exist in this pre- 

 paration, and a relation, hitherto unobserved, has been shown 



Ca 

 to exist between the ^^^ thresholds of these muscular tissues and 



the effects of adrenaline, ergamine, and so forth upon them. 

 Whether this relationship has more general application, or is 

 limited to the tissues employed in these experiments, is a 

 questioi;! which awaits further investigation. 



Conclusions. 



Oa 



1. There exists, in the fly's intestine, a gradient of ^ 



thresholds, above and below which contractions or peristalsis 

 cannot occur, and between which lies an optimum ratio. The 

 threshold and optimal ratios increase from below upwards, 

 being least in the posterior rectum and highest in the distal 

 intestine. 



2. Curari and atropine in 1 : 1000 solutions are devoid of 

 effect upon the contractions of the excised fly's intestine. 

 Nicotine and pilocarpine exert long-delayed inhibitory action. 

 Codeine and chloretone in 1 : 1000 solutions immobilise the 

 preparation' immediately. 



3. Veratrine immobilises the fly's intestine, but without 

 evidence of prolonged contracture or increase of tone. 



4. Adrenaline stimulates the preparation in such a way 



Ca 



as to suggest that the -7T7- thresholds have been lowered. 



5. Ergotoxine, ergotinine, ergamine, and digitaline 

 inhibit the preparation. In very dilute solutions they may 

 stimulate the rectal movements. Their effect is such as to 



suggest that tlie-^- thresholds have been raised. 



6. Pituitrine exerts a dual action, the initial effect being 

 stimulation, the later effect inhibition. 



7. In its reactions to the above-mentioned drugs the muscle 

 of the fly's intestine resembles its functional similar (the verte- 

 brate smooth-muscle fibre) rather than its structural similar 

 (the vertebrate striated muscle fibre). 



References. 

 (1) Lowne, B. T. : '*The Anatomy, Physiology, Morphology, 

 and Development of the Blow Fly," London, 1890- 

 1892, vol. i., p. 283. 



