EE VIEWS. 
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says 11 that the tubes forming the wood are pervious to fluids in their young 
state, hut that their walls soon become thickened by deposits of lignine, 
and in the heart- wood of trees their cavities are obliterated.” Another 
objection, too, has been raised against Mr. Spencer’s idea, viz. that the spiral 
vessels frequently contain air within them. But, as Dr. Pettigrew very 
justly observes, this is an objection taken purely from the known condition 
in animal life ; and there is really no reason why the vessels of vegetable 
tissue might not contain air as well as their circulatory fluid. Besides, there 
are many other analogies between the vessels in animals and plants which 
are dwelt on at some lengfh by the author. On the subject of the rythmic 
action of the heart, which is so peculiar, the author refers to the rythmic 
action that is seen in certain plant-cells. The observations of Herr Cohn 
show that in Gonium pectorale and other plants the contractions of the 
vacuoles, like the contractions of our own hearts, take place at regular 
intervals. u The contractions (says Sir James Paget, in his Croonian Lecture) 
and the dilatations occupy equal periods, as do those of our own heart 
ventricles, and when two vacuoles exist in one cell their rythms are alike 
and exactly alternate, each contracting once in about forty seconds, and the 
contraction of each occurring exactly mid-distance between the two successive 
contractions of the other.” Thus we see the exact counterpart in plant-life 
of a function which we used to consider at one time essentially an animal 
one. And this leads on the author to speak of the various forces of osmose , 
and to explain by very simple experiments the manner in which they act on 
the living plant ; and thus he passes to consider Spencer’s theory of the ac- 
tion of the wind in bending plants, and by this carrying on the circulation ; 
next to the question of the action of syphons, and finally to the so-called 
circulation in metals in Seebeck’s discovery ; and with his remarks on this 
subject he terminates the history of the circulation in plants. Indeed, this 
part of his book will well repay the reader, for it is a lucid and fall account 
of what has been done in the matter. 
It is on the next portion of the work that the author displays his powers 
to best advantage, for it is here that he is most at home with his subject. 
And indeed he has collected together a number of facts, many of them from 
his own original labours, such as to render the merely popular reader some- 
what aghast at the immense range of the subject, He deals with the lowest 
type of circulatory system, and shows the mode of its operation ; and then 
he passes on to consider the higher forms, until at last, after over one hundred 
pages engaged in the discussion of those subjects, he comes to consider the 
forces of the human circulation, and the organs in, or through, which these 
forces are exerted. All through he has splendidly illustrated his subject ,* 
and we find him, in all that relates to the structure of the human heart and 
its valves, giving us an amount of information, and putting it in so easily- 
digested a form, that by this fact alone, if we were ignorant of the valuable 
papers he has published on the subject, we could see that he has not ap- 
proached the question for the first time. But he has gone over and over it, 
so that at last, when he is speaking, there is no uncertainty about what he 
says ; but, on the contrary, it is all clear and distinct, either the known or 
unknowable. Of course our space will not permit us to give even a sketch of 
the method he pursues, but it will allow of our recommending certain portions 
