Physiology of the Heart. 145 



action is manifested ; but when this begins it quickly and 

 steadily rises to a maximum. (2) It causes diminished 

 diastolic relaxation ; but especially characteristic is the 

 effect on the systole which is both more perfect and when 

 complete more prolonged than usual. (3) The ventricle is 

 always arrested in most pronounced (tetanic ?) systole and 

 then always looks very small aud pale. It is inexcitable. 



The action of drugs on such sensitive hearts as those of 

 the Selechians was found correspondingly rapid. The action 

 on the isolated heart was also more rapid than in the heart 

 in situ, as was to be expected. 



In many cases the first effect of a drug was to arrest the 

 auricle proper, leaving the sinus extension comparatively 

 unaffected. 



Our North- West Prairies, their Origin and their 

 Forests. 



By A. T. Drummond. 



The origin of our North-West prairies may be traced to 

 two causes, one long since removed, the other still operating. 

 During the pre-glacial and glacial periods, the inequalities 

 of the surface over vast tracts of the country in our North- 

 West were filled up by clays and gravels, and more or less 

 levelled. These clays were, to some extent, subsequently 

 re-arranged underwater, and at the same time new material, 

 chiefly gravels, sands and sandy loam, was deposited. Then 

 these extensive tracts were gradually upheaved above the 

 level of the water or were left dry by the fall in the water 

 through the diminution in the sources of supply, or by the 

 greater facilities afforded for rapid drainage. There had 

 been previous upheavals during the drift period, and there 

 were traces of resulting vegetation. The second cause, then, 

 or immediately previously, came into play, and consisted in 

 the annual growth and decay, for long periods of time, of 

 grasses, sedges and aquatic plants generally, over extensive 

 areas in the shallower waters and along the shallow lake 



